For the seventh night in a row, Pete Black felt alone and isolated in the middle of the Bavarian forest. It was the summer of 1995, and one of the most stressful experiences of his life. Normally his nerves were pretty resilient. But camping in a giant, thick spruce forest, surrounded by more than 1,500 anti-racist activists from 18 different countries, he was gripped by a fear that he would be found out. Part of the reason for his paranoia was the knowledge that if anything were to go wrong, there was no effective back-up for miles around. He had no mobile telephone or tracking technology. He was on his own and the fear of what might happen if he attracted suspicion was terrifying.

Black was in Germany for a summer camp organised by the YRE. By now, he was heavily involved in their campaign, a key London organiser. The camp, in a big clearing in the forest, was designed partly to be a holiday for European anti-racist campaigners, a place they could meet each other, socialise and let their hair down. There was a disco tent, a chill-out area and a marquee where attendees could be entertained by some German rock bands.

But this was also a political gathering, a meeting of minds where ideas could be swapped between anti-racist activists from across the continent. The location of the camp deep in this particular forest was no coincidence. It was a two-fingered salute to neo-Nazis, who claimed this part of Germany as their heartland. The camp was protected around the clock against attacks from fascists, with regular patrols around the perimeter. ‘I had to do night-time patrols as well,’ Black recalls.

One corner of the campsite was taken over by the Black Bloc, hard-core anarchists who, Black says, had brought firearms with them. They were notoriously frosty to outsiders. One night, the activists were woken by gunshots. The next day, the anarchists insisted it must have been hunters shooting wild boar – or Nazis firing bullets into the night sky to scare the campers. Whoever was responsible for the shots, they only added to the anxiety gripping the undercover police officer.

‘It was scary, an absolute nightmare – I can’t begin to explain it,’ he says. Black’s fear was compounded because he had made a crucial error that made it far more likely he would be exposed as a police infiltrator. He had failed to anticipate that he and the other activists would be sleeping beside each other in a large tent. Black feared he would talk in his sleep, and he was terrified he would inadvertently mutter something about being a police officer when dreaming.

Back in England, when campaigners stayed at his flat, Black had a technique to stop himself from blurting out something incriminating in his sleep. ‘No matter how many bedrooms you had they would always – bar the occasional female – camp in the lounge, so when I went into the bedroom, I could slam a chair under the door handle and sleep.’ In the depths of the Bavarian forest, that was not an option.

‘I could not sleep properly for a week,’ he says. ‘Your weakness is always when you’re asleep. With the benefit of hindsight, I should have brought my own tent. But I had never built into my cover story anything about a tent. If you brought your own tent, but did not know how to use it, it would have looked like you had deliberately brought a tent to be by yourself.’ He had no choice but to bed down with five other activists, bury his head in his sleeping bag and hope for the best. ‘I thought, “Fuck it, go with the flow,”’ he says.

Black says that week in Bavaria ‘was the most intense pressure’ over a sustained period of time he had experienced on the job. ‘You are undercover trying to pretend you are enjoying yourself, in this huge drinking environment,’ he says. If activists had been harbouring suspicions about Black, he knew the remote camp was the ideal opportunity to confront him. The camp organisers had taken and photocopied everyone’s identity documents. ‘I thought: if it really did go tits up, my identity had to be perfect. I could not get out of the camp as they had my passport.’

Underneath his calm exterior, Black was riddled with paranoia. He worried about the most improbable of scenarios. For example, when he was much younger, Black spent a few years living in a German village. Now he was worried that someone from his younger days might by sheer coincidence attend the camp and recognise him. He kept rehearsing this and other unlikely scenarios in his head, preparing himself for the unexpected. ‘What you do in the SDS is you hope, if not pray for the best,’ he says. ‘But you always plan for the worst.’

Black had himself to blame for finding himself in the German forest. He had insisted the SDS should let him travel to the camp, even though the squad had until then never dispatched one of its spies abroad. He had gone through ‘a world of pain’ to get special approval from Special Branch and the German police authorities. By then he had risen to become the secretary of a branch in the YRE and he thought it would have been deeply suspicious not to attend the camp.

‘Everyone knew that I had German connections, with my mother being German,’ he says. ‘It was beyond belief that I would not go.’ For the SDS, the experiment in foreign espionage was a gamble. Special Branch bosses stipulated that another officer had to travel with Black and meet with him regularly, but it turned out to be too risky for Black to slip out to speak with his handler.

‘We had no contact during the week,’ he says. Instead, Black’s handler spent the week relaxing on the SDS expense account in a nearby hotel.

Given this was the first foreign mission for the SDS, the unit decided Black should be accompanied by a particularly senior officer – a man who had recently rejoined the squad. And so it was that as Black was sleeping fitfully through the night, terrified at the prospect of being exposed, Bob Lambert was taking in the scenery at a safe distance. ‘I was – I kid you not – in the middle of an isolated Bavarian forest; he was holed up in a hotel a few miles away enjoying himself,’ says Black. Even though Lambert was some distance away, he was a reassuring presence for Black. The older man’s reputation preceded him. ‘He did what is hands down regarded as the best SDS tour of duty ever,’ Black says.

Under the deal Lambert struck with German authorities, Black was required to provide an extensive report on the country’s home-grown activists – in addition to his routine work for the SDS. He was under pressure to record everything that was happening around him but felt unable to resort to writing down notes.

‘Where are going to hide them – in your underpants or something?’ he says. ‘You can’t stick a report in your underpants, you are in a tent sharing it with people. You do it from memory, you remember absolutely everything. That’s old tradecraft – you never write things down. They would rather you lose intelligence.’

Once his adventure in the forest was over, Black spent days downloading everything he could recollect from the camp. He compiled and delivered a series of reports on the YRE campaign and their connections on the continent. He says that because he spoke German, and could converse with native activists, he managed to provide the host country with high-grade intelligence. The Germans felt the SDS had done them a ‘huge favour’, he says.

Lambert and the rest of the senior command felt the trip was a success. It paved the way for other undercover officers to travel abroad. One went to France with the Anti-Nazi League, while the following year Black travelled to another summer camp (this time, with his own tent) in Greece. It was the start of a trend. Within a decade, there would be an almost constant exchange of undercover police officers across Europe posing as activists.

Back in London, Black had moved on from the small Kingsway anti-fascist group. He was now secretary of the Hackney and Islington branch in London of the YRE, with access to much of the group’s paperwork and the revolutionary party that pulled its strings. For Black, membership of Militant Labour, which controlled the anti-racist group, was crucial.

‘There is no way on God’s earth that I could become a branch secretary of the YRE without becoming a member of Militant,’ said Black. Militant’s heyday had been in the 1980s, when it was a household name. Its Trotskyist supporters infiltrated the Labour Party, running a covert ‘party within a party’ as part of a strategy to radicalise Labour. Then known as the Militant Tendency, it was most well known for taking control of Liverpool Council and making a defiant stance against Margaret Thatcher’s policy of cutting public funding. During the course of the decade, Labour leaders gradually expelled Militant operatives from the party until, in the early 1990s, they were forced to come out into the open to establish an overt political group, Militant Labour. By then its influence was fading. When in 1997 it changed its name to the Socialist Party, Black remained embedded.

Once inside Militant, Black turned himself into an ‘intelligence-gathering machine’ for the SDS. He continuously cultivated his activist fake persona, which he rightly believed would be crucial to his success. Black’s alias was a mixture of ‘Mr Angry’ and ‘Mr Hard’, a tough guy who could handle himself in a fight. He wanted to be known as a character who ‘was angry with the whole world’. ‘I could bristle with anger,’ he says. Hannah Sell, a YRE leader, remembers Black as ‘a bit hot-headed and macho’. She says the newcomer ‘tended to argue for brawling’ with the far right. ‘We explained that defeating racist and fascist groups is a political task which required patient campaigning in working-class communities, rather than street fighting.’

Like all SDS officers, Black tried to anchor his constructed personality in life experiences from before he was deployed. ‘You use things from your real life to incorporate into your fake life, but you don’t use something that hurts or is too personal,’ he says. ‘The only thing I found all too close to home was the idea of making my mum an alcoholic. Instead I made my fake dad an alcoholic and gave that as the reason he had been beating me up. I needed that because I knew that at some point I was going to have to explain how it was that I could fight so well. The answer was a simple one. I told people that if they had a father who beat them up every day, they would learn to fight pretty quickly too.’

Every aspect of an SDS officer’s legend had a purpose. For example, Black pretended to be dyslexic, even though he was perfectly capable of reading and writing. He even made sure to deliberately skew a test before his deployment, to give the impression that he had the disability. ‘It’s something you can teach yourself,’ he says. ‘In about half an hour I can turn it on.’ The main reason for the faked dyslexia was that Black needed an excuse to attend Kingsway College as a mature student. ‘My story was that I was going back in order to get my first ever GCSE and to make my German mother proud,’ he says. ‘That gave my cover a real emotional pull to it. I said I’d grown up thinking I was stupid and not doing very well at school, but had come to realise that this wasn’t the case.’

Black’s purported dyslexia had other advantages, too. SDS officers liked to emphasise their vulnerabilities, generating sympathy from people they met. Black wanted activists to be taken in by the sad story of a man held back by his disability, despite an innate intelligence. He wanted to come across as a frustrated soul who needed nurturing politically. He was soon being invited to workshops to be taught about Trotskyism.

‘I used to go to educational classes every second Sunday unless there was a demo,’ he says. ‘These were one-on-one sessions where you would be taught by people, sometimes from the top of Militant. You would go round to their houses and talk about Marx or Engels. It was a complete nightmare because I was not interested in that stuff at all, yet I still had to learn it and show that I was willing to be educated to some degree. That was important in order to gain their trust and respect.’

He adds: ‘But for me the dyslexia was a huge bonus. It meant I could refuse to be given the large books on theory. It meant that I had a good reason to stay at the level where I was. They’d asked me how I was getting on with a book and I’d say that I had only made it up to page three so far and there was not a lot they could say about it. It was a very effective way of fending people off.’

Black also took care to maintain the appearance of a revolutionary leftist. To activists, the combination of a ponytail down his back and balding patch made Black stand out – one would go as far as to say he looked ‘like a loser’. There was a sense in Militant circles that Black was eager to please – a reputation the operative wanted. He knew that his best chance of gaining the trust of the group was to do many of the boring jobs other campaigners always wriggled out of.

Sell remembers how Black did a ‘lot of the donkey work’ and never turned down a request for a favour. Like almost all SDS officers, Black owned a van – it was the signature prop for the squad, allowing its operatives to make themselves useful by ferrying activists around. ‘The van was good cover,’ Black says. ‘I did a lot of photocopying for the campaigners and I carried things around in the van. All the groups we targeted were poor and never had any transport so having a van made me instantly valuable.’

The SDS had provided Black with a basement flat in Furlong Road, a quiet residential street in Islington. He chose that location – rather than an apartment in Hackney, where Militant’s headquarters were located – to minimise the likelihood activists would pop around unannounced. During the two years he lived there, Black tried to keep the place ‘clean and tidy’ and fill it with sufficient furniture to avoid it looking empty. The leftist campaigners appear to have been unimpressed. One activist recalls Black’s flat as being ‘a bit tacky, like a student flat’, while another, Greg Randall, says it looked ‘grotty’.

For a job, Black called in a favour from someone he knew who worked in a local school for children with special needs. ‘I said to her that I would like to volunteer to work at the school. I said I didn’t want to lie to her, and that I would be using it as cover of sorts.’ The woman knew Black was a police officer, but not much else.

The friend agreed, and Black was told he could help out around the school, and receive free dyslexia lessons in return. The school authorities had no idea about his true role. ‘They didn’t know that I was an undercover police officer and they didn’t know that I didn’t have dyslexia either,’ he says. With regular access to the school, Black contrived a somewhat different explanation for his friends in left-wing campaigns. Instead of telling them he occasionally volunteered at the school, he claimed to be its handyman. The two sides – the school authorities and his activist friends – had a different concept of what he was doing there.

‘As long as the two never met up for a longer interrogation, it worked,’ he says. ‘You need to have a job so that people don’t wonder why you have enough money to do things they might not be able to do. But it can’t be a regular job. Somehow you have to be flexible enough to be able to take time off at short notice whenever there is a demonstration or a meeting and that kind of thing. You need to be able to move things around.’

The SDS always stressed the importance of a watertight cover story. From its long experience in political espionage, the unit knew that campaigners had their own, often sophisticated, methods of counter-surveillance. Suspicious individuals would be followed home or subjected to minor interrogations. Some activists even had access to the tools of the state to research the backgrounds of newcomers who did not seem quite right. Many Militant campaigners, for example, worked in the public sector, and could quietly run checks on government databases to verify whether people were who they claimed to be.

Managers in the SDS arranged for fake national insurance numbers and tax records to be drawn up and inserted into the official bureaucracy for each of their undercover officers. ‘This is not Mickey Mouse cover,’ Black says. ‘You have perfect Inland Revenue records stretching back, usually involving some kind of manual labour so that there are no bank transfers and so on. If you were to look at it, you would not see anything wrong.’

And in this particular battle, police had the upper hand. Unbeknown to public-sector employees who were running database checks on the sly, there was a silent trigger on all official records belonging to SDS officers. It meant that the moment an activist pulled up a file belonging to an SDS officer, an automatic alert was sent to the unit. This was how Black discovered that secret background checks were being conducted on him, around the time he was being considered for the post of a YRE branch secretary.

This particular incident was not too concerning. Campaign groups routinely looked into people they did not know too well, and Militant was especially paranoid. ‘They had infiltrated the Labour Party and expected to be infiltrated themselves,’ Black says. He also felt he had taken sufficient precautions. The rent for his flat, for example, was paid in cash, and later recouped from the police. His van was registered to the school, so nothing suspicious would pop up in a search of records at the Driving Vehicle Licensing Agency. Believing that activists could even get access to the Police National Computer, the SDS had ensured that its spies had fabricated files listing some past misbehaviour. A false criminal record was created on Black’s undercover identity and inserted into the national database. ‘You have to have a PNC record with some violence on it. Not too much, but a little bit,’ he says.

These safeguards were all useful, but Black knew what really mattered was his ability to make friends. He threw himself into socialising, determined to persuade them that his fake persona ‘was the real thing’. The social life was ‘pretty unrelenting’, Black says; often activists went to the pub after a meeting or demonstration and carried on drinking in one of their flats until the small hours.

‘I had a really good time with my targets and enjoyed their company enormously – there was a genuine bond,’ he says. ‘There’s a sense of comradeship in what you have done together, the battles you’ve had, your battle scars and what you have been through.’ But deep down, Black knew that these were not the sort of people he would associate with in his real life and he always remembered his ‘overarching loyalty’ was to the SDS. ‘Would I have been friends with any of these people, would I wish to be friends with any of them? Not a single one of them.’ When Black felt himself becoming close to an activist, he tried to remind himself he was just ‘pretending’; that the bond, however strong, had a strictly utilitarian function.

But it was not always easy for Black to maintain his ruthless detachment. There were times when he realised his friends were genuinely good people. One day, Black needed to take some time off. His wife was giving birth to his child and so he needed an excuse to spend fewer days living undercover. In his real life, when he was a child, Black’s parents had divorced and his mother took to drinking heavily. In the end, his grandmother had helped bring him up as a sort of surrogate mother. Around a decade earlier she had fallen ill with cancer.

It was a biographical detail that Black integrated into his cover story – with a twist. In order to manufacture a reason for his time away from London, Black told friends that his mother in Germany had cancer. It was a lie, but it enabled Black to draw on the genuine emotions he felt when his grandmother had fallen ill. By resurrecting the illness that had ravaged his grandmother 10 years earlier, and pretending it was now affecting his mother, Black could speak convincingly about the physical and emotional toll the disease was taking on him.

Every time Black needed a break from undercover life, he reused the fabricated tale about his mother’s cancer. The fiction lasted around two years. His friends became more concerned for Black, who they believed was going through a hard time. He still has the sympathy cards, signed by more than a dozen activists, that he received whenever he told them he was off to Germany to visit his gravely ill mother. One of his friends wrote: ‘Peter, just a thought from the branch. We heard about your mum and this is just a note to say we’re thinking about you and hope she’s doing OK.’

By the middle of his deployment in 1995, Black had settled into the weekly routine of an undercover SDS officer. Early on a Monday morning, he woke up in the Furlong Road flat and drove through rush-hour traffic to the home of his real family, outside London. Once there, he went into the study to write up a report into what the activists had been doing over the weekend. Once it was finished he drove back into London, made his way to one of the unit’s safe houses in the afternoon and hooked up with the rest of the squad for one of their regular weekly meetings.

‘The work of the day was to give a debriefing on the weekend,’ he says. After the meeting, Black often went for a drink with the squad and then returned home to be with his wife and kids. It was often a long journey; SDS officers took circuitous routes everywhere to ensure they were not being followed, a process known as ‘dry-cleaning’. Once home, he says, ‘you would be lucky if you could stay into Tuesday afternoon or evening’. It was the briefest of respites: a quick, sobering dip into his old identity – that of a police officer, father and husband – before driving back into town to reassume the identity of an unwavering Militant campaigner and bachelor.

Black liked to be back at his Furlong Road flat by the late afternoon, giving the impression he had spent a day doing odd jobs at the school. He was in the school for two days a week. ‘It’s a real role – if the activists came to the school, you would be there,’ he says. The rest of the week was spent with the activists, trying to pick up intelligence about forthcoming protests, either that weekend or in the future. On Thursday afternoons, Black attended the second regular SDS meeting of the week, at which the undercover officers were expected to brief their bosses on any protests coming up that weekend.

Black tried to be at his Furlong Road flat on Friday nights, too, in case activists came round. He spent the weekends involved in political activity, attending protests, selling Militant’s paper on street corners or socialising with campaigners. His boss Lambert placed great emphasis on making friends and going out. It made for more reliable cover. Of course Black also knew that SDS officers regularly slept with women activists to build the credibility of their persona.

Unlike the likes of Lambert and Chitty, he never developed any long-term relationships with women when undercover, but he did have sex with two activists. It is a subject he talks about in a matter-of-fact way. He argues it would have been virtually impossible to do his job without occasionally sleeping with women.

The unofficial motto of the SDS was ‘By Any Means Necessary’, and all operatives knew that sex was one tactic in their repertoire. ‘Basically it’s just regarded as part of the job,’ he says. ‘It’d be highly unlikely that you were not having sex.’ It was so widespread that out of the 10 SDS officers undercover when Black was deployed, only one did not sleep with campaigners. That included the small number of women in the squad, who had sex with male activists.

There was no specific rule against having sexual partners. It was so commonplace that, he says, it was barely remarked on. ‘Among fellow undercover officers, there is not really any kudos in the fact that you are shagging other people while deployed,’ he says. Having sex with campaigners was something that – either implicitly or explicitly – had the blessing of those running the SDS. They knew it was going on and did nothing to stop it. Indeed, Black says that while sex was considered acceptable, one unofficial rule was that operatives should ‘never fall in love’ with their targets.

‘When you are using the tool of sex to maintain your cover or maybe to glean more intelligence – because they certainly talk a lot more, pillow talk – you would be ready to move on if you felt an attachment growing,’ he says. ‘The best way of stopping any liaison getting too heavy was to shag somebody else,’ he says. ‘It’s amazing how women don’t like you going to bed with someone else.’

But there were occasions when the undercover officers strayed too far. When Black was undercover, he was not aware that anyone in the unit knew that Lambert had secretly fathered a child. However, they did know of another former SDS officer who fathered another child during a short-lived relationship. Like Lambert, he vanished from the lives of mother and child when his deployment ended. The mother brought up the child on her own, while the SDS officer continued his career in the Special Branch. The woman remained politically active, enabling the former SDS spy to periodically check up on her by reading confidential reports about her campaigning.

The spy watched from afar as the child grew up. He was reputed to have been agonised by the separation from his child. The story was recounted by Lambert to new recruits like Black without even hinting that he too had fathered a child undercover. Lambert even had the gall to criticise the officer for behaving unprofessionally. He told Black that the moral of the story was that he should always use contraception when sleeping with political campaigners.

Black’s wife knew that he was undercover, but was unaware of the details of his work and certainly had no idea he was sleeping with other women. His long absences and unforgiving schedule left virtually no time for his wife and two children. For more than four years, he was away for six days a week. Sometimes, during school holidays, he found a way to spend more time back at home in the real world. But it was never enough. Black paid a personal price for ‘trying to be the best SDS officer I could ever be’. He admits his wife had a ‘very difficult time’. ‘The fact I was working so much eventually caused the break-up of my marriage,’ he says.

The top brass at the SDS, however, valued his dedication to the job. Lambert said in an early appraisal that Black was self-motivated and a hard worker who ‘demonstrated an innate professionalism’. The next year Lambert offered yet more praise: ‘Operating in a hostile environment where one slip can have serious implications for the officer and the team, [Black] has again demonstrated essential qualities of sound judgment and ingenuity. Combining, as he does, these qualities with a single-minded determination to succeed, it is a pleasure, and no real surprise, to report that his efforts have again been rewarded with excellent results.’

The results that Lambert was referring to included regular updates on what was going on in anti-racist groups across London, as well as the inner workings of the YRE and Militant. Black calculates that Special Branch was keeping files on around 100 members of the YRE, Militant and other anti-racist campaigners at the time. The files on individuals would contain reports of their activities at protests, other more general intelligence and information from sources such as newspaper articles. It would include, for instance, where they lived, where they worked, and whom they were friendly with in the campaign. Black himself opened up new files on around 25 campaigners he believed needed to be monitored.

Each file on an individual required an up-to-date photograph and Special Branch had an uncanny ability to acquire photographs when it needed them. Official images were available to the squad – from driving licences, passports and suspect mugshots taken inside police stations. Upon request, Special Branch could also deploy sniper-like photographers with long lenses. Black recalls arranging for one such snapper to be hidden in a van outside Conway Hall in London to capture images of everyone who attended one of Militant’s conferences. The SDS also had access to the network of CCTV cameras that in the mid-1990s were proliferating across the capital. When Black travelled on the Tube with activists, Special Branch acquired footage from London Underground, enabling the officer to identify who he was with.

While Black’s job was primarily to hoover up intelligence, there were opportunities for him to broaden his mandate. On one occasion this enabled him to realise a schoolboy dream. For decades, surveillance of radical left-wing groups had been a staple feature of MI5’s work. Government ministers had, since the 1950s, ordained that the Security Service could spy on any individual who might undermine parliamentary democracy, national security or the economic wellbeing of the country. Critics complained that MI5 was effectively spying on individuals for having opinions that the government disliked, using a definition of subversion that was so loose that it included anyone who was exercising their democratic right to protest.

The point is made by Annie Machon, a one-time MI5 officer who resigned in protest at its activities. She says that from 1952: ‘MI5 and subsequent governments used to argue that all members of certain parties – such as the Communist Party of Great Britain or later the bewildering array of Trotskyists, with names like the International Marxist Group, Workers Revolutionary Party, Revolutionary Communist Group, anarchists and the extreme left – were threats to the security of the state or our democratic system. This in itself is a contentious proposition. None of these Trotskyist groups was cultivating Eastern bloc finance or building bombs in smoky back rooms but were instead using legitimate democratic methods to make their case, such as standing in elections, organising demonstrations and “educating” the workers.’

During the cold war, MI5 devoted huge resources to spying on left-wingers; tapping phones, opening mail and running agents within organisations. For a long time, Militant was a prime focus, because of the threat it posed to the Labour Party. But by the early 1990s, MI5 was becoming less interested in domestic political threats. It was becoming harder for the spooks to justify spying on groups that, by any objective view, posed little or no threat to the foundations of the state. Militant, whose membership was in any case beginning to dwindle, was operating as an open political party. According to Machon, MI5 began to downgrade its work spying on revolutionary left-wing groups around 1993. By late 1995, according to one account, MI5 was allocating only one of its officers to monitoring so-called subversives.

Lambert and others in command of the SDS spotted an opportunity. As MI5 retreated, the SDS could occupy the ground the security services were vacating. In one confidential briefing memo, Lambert noted how MI5 was winding down its ‘active role in respect of domestic subversion’. The SDS offered to channel intelligence about Militant to MI5, keeping them abreast of what was going on in the group.

The offer was accepted and, in 1995, Black began a dual role, working partly under the command of the SDS but also as an official informant for MI5, with his own code number: M2672. Lambert, who believed Militant was ‘one of the most insular groups ever penetrated by the SDS’, was impressed that one of his spies was providing intelligence for the Security Service. Black was raising the stock of the squad in official circles and allowing senior officers like Lambert to punch above their weight. When Black produced a report on a large number of Militant activists, and handed it over to MI5, Lambert complimented his efforts. ‘This performance, both in terms of content and presentation, was of the highest calibre and brought considerable kudos to the team,’ he wrote. In another Special Branch document, Lambert noted how the Security Service was ‘an appreciative consumer of the unique high-grade intelligence’ provided by Black.

The spooks were genuinely grateful for SDS assistance. MI5 gleaned most of its intelligence not from undercover officers, but informants, many of them paid. These individuals, known as agents, were given a rudimentary instruction into espionage tradecraft by MI5, which then cultivated them as sources. According to one account, MI5 recruited around 30 Militant members to inform on their comrades over a 30-year period during the cold war, although by the early 1990s there were only a handful of snitches left. As with all informants, their reliability varied wildly.

When Black noticed that MI5 was holding erroneous intelligence about Militant, he assumed the Security Service must have been fed by a dodgy agent. ‘I started to realise that there was a spy in our midst,’ he recalls. ‘I decided I was going to try and spot their agent. In the event, it did not take very long.’ Rather worryingly, Black says the MI5 agent stood out like a sore thumb.

‘He was doing things like only turning up to meetings when something really interesting was being talked about. Those sort of things made him stand out,’ he adds. Acting on his instincts, Black decided to confront MI5 and ask them: ‘Is he one of yours?’ The question sparked an immediate reaction from the MI5 officer in charge of running agents. The agent handler left Thames House, MI5’s imposing headquarters on the bank of the River Thames, for a hasty meeting with Black, Lambert and other Special Branch officers in the safe house in Beaumont Court, Chiswick.

It felt like a showdown. At first, the MI5 officer refused to give anything away about the suspected agent. ‘They tried to bluff me and said they could not confirm it, but they would take [my suspicions] on board,’ Black says. But the SDS officer was characteristically stubborn, insisting he had the right man. Eventually, Lambert and the other officers were asked to leave the room. Black and the man from MI5 remained, for a ‘frank discussion’ about the Militant activist identified as an agent.

‘I said to him that I knew it was him, and if he did not agree that the man was an agent, I would expose him at the next Militant meeting. The handler replied, “OK, he is ours – don’t blow him out of the water but we will get rid of him.”’ The MI5 agent was withdrawn a couple of months later. Black felt the move was long overdue; if he had managed to work out the informant’s true motives, then so too could other members of Militant. They might easily have fed the agent faulty information, knowing it would be passed on to MI5.

‘The biggest problem was that his intelligence reports were shit,’ Black says. ‘He was giving information that was inaccurate about people, which meant he might well have been giving out inaccurate information about me as well.’ Later, Black’s managers told him he was the first SDS officer in history to catch out an MI5 agent. ‘So it was big kudos for the team,’ he says. ‘The Security Service was grateful.’ Later M15 came over and presented Black with a shield on a wooden block. It was engraved with MI5’s crest, and the service’s motto – ‘Regnum Defende’, Latin for ‘Defend the Realm’ – at the bottom. Black was told he was the only SDS officer to receive such an accolade. It was a moment to remember, a standout episode that Black hoped would make it into the annals of SDS folklore – the kind of success that would have made Conrad Dixon proud.

Sitting in the Chiswick safe house with Lambert and his other SDS colleagues, Black soaked up the convivial atmosphere. ‘I felt proud at the time. It was some sort of recognition because the Special Branch does not really recognise the work you do that much,’ he says. It was an especially satisfying moment for Black, who always wanted to work for MI5. The shield still hangs on his wall in his study at home.

Things were going well for Black. His career was on a high and he should have been proud of his achievements. But in fact he had begun to experience deep misgivings about his deployment. His final mandate as a spy would leave the normally decisive officer grappling to discern right from wrong.