The highlight of my political career? That’s an easy question to answer. It was the period I served as the Secretary of State for Defence, between 1995 and 1997. This wasn’t so much because I occupied one of the highest political offices, though I was certainly proud on that score. It was mainly to do with the people I dealt with. Some were civil servants, many were in the military. All were high-grade individuals – intellectually rigorous with tremendous personal qualities of bravery, enthusiasm, commitment and, in most cases, personal loyalty. So it was an absolute pleasure to run into such types again while visiting the sites and developing the themes of this section on the ‘Defence of the Realm’.

I was also reminded of how little I knew, really knew, despite supposedly being all-seeing and all-knowing as Defence Secretary. Of course, I was made aware of current secret research and covert operations but that was usually on a ‘need to know’ basis, because they required my authority or funding. On my first day in the defence job I wasn’t presented with a dossier listing all the highly classified activities in which the government and the military were engaged, and I rather doubt that the prime minister was either.

This is how the world of state secrecy operates, by ensuring that not too much information is accumulated in a single place or a single mind. That applied to me, as Defence Secretary, and also to a person such as twenty-two-year-old Roger Darlington in 1971, when he was pitched into the top-secret world of Cold War espionage alongside tight-lipped American spooks. This was at Cobra Mist, a hush-hush installation on the Suffolk coast patrolled by military police with big dogs and even bigger guns. Roger was a technician responsible for processing highly classified data but, having signed the Official Secrets Act, he thought it safest to say he was just a cleaner when quizzed by curious locals in the village pub.

Cobra Mist was just one among a plethora of secret sites located in a remote spot called Orford Ness, well away from the public gaze. The various research and development projects that took place there closed down well before I joined the government, so although I had heard of Orford Ness I didn’t appreciate just how vital it had been to the defence of the realm. Many innovations, great and small, were tested and perfected in these windswept huts and labs, by men and women who perfectly fitted the epithet ‘boffin’.

They were scientists, academics, engineers and military personnel, and they had a genius for applying their field of expertise to defence and military imperatives – characters such as Professor John Allen, now ninety-five and one of the last of his generation, who tracked the flight paths of dummy nuclear bombs as they were dropped over East Anglia (he admitted that at least one landed in someone’s back garden). For the most part this vital work wasn’t glamorous. It did not yield instant results but proceeded painstakingly, by trial and (frequently dangerous) error. The real revelation, for me, was just how dangerous it was on occasion. I knew that nuclear weapons had been tested on Orford Ness but the official line has always been that there was never any chance of a catastrophic accident. One of my witnesses, a man who stress-tested nuclear bombs, told another story.

His admission shocked me but I reflected later that it wasn’t so surprising. In military research, as in civilian life, strategies and policies are often riddled with holes. The fate of Imber, the little village on Salisbury Plain that fell victim to Britain’s mighty war machine, is a brew of cock-up and conspiracy – in what proportions no one can be sure. I had been there before, again in my capacity as Defence Secretary, but the village had made a negligible impression on me. It was a training area, nothing more. I had no idea of the continuities that had been broken, the families disrupted, by what happened here at the end of 1943. The irony is that Imber embodied, in its longevity and peacefulness, the very qualities we went to war to protect. On my return, I was engulfed not just by the story, but by the spirit of the place – forlorn, yes, but not quite extinguished. It lives on in fragments of buildings, in the church especially, and in the old Imber families who walked its ghostly streets with me.

If Imber moved me, the nuclear bunker in Cambridge left me perturbed. From the early 1950s right through to the end of the Cold War, it was assigned a vital role in our civil defence strategy as a Regional Seat of Government (RSG) – a sort of mini-Whitehall – should Britain suffer nuclear attack by the Soviet Union. When the country was laid waste by radioactive fallout and physical destruction on an unimaginable scale, it was the chaps in the RSGs who would keep our peckers up by broadcasting reassuring news, playing stirring songs, and plying us with biscuits.

The idea was absurd, the planning farcical. The story of the RSGs would have been funny if it hadn’t been so serious. For while bewildered personnel on war exercises were wandering through provincial towns asking for directions to the local top-secret bunker, the Cold War was hotting up. It reached boiling point with the Cuban Missile Crisis of 1962. It was fascinating for me to revisit this seminal episode in twentieth-century history. Though I remember it, I didn’t understand it and felt the enormity of it principally through the reactions of my parents. Here, I was able to meet people who were there, at the sharp end of history.

One was a crew member of a nuclear-armed British bomber on just a few minutes’ notice to attack the Soviet Union. As the bombers stood at attack-readiness on the runway, he advised his wife to jump in the car and drive to the Isle of Skye. ‘I think you’ll be safe there,’ he told her. Meanwhile, he contemplated a mission from which he almost certainly would not have returned. Some 4,000 miles away the commander of a Soviet submarine was caught in America’s naval blockade of Cuba. Hiding far beneath the surface, out of radio contact, he heard explosions and did not know whether the Third World War had started – and, if it had, how to react. ‘The situation was very difficult,’ he told me, with considerable understatement.

Such testimonies were priceless and validated the whole approach of Portillo’s Hidden History of Britain in getting people who were there to tell it how it was. For this section, in particular, I met a great many people and in some cases they were individuals I would almost certainly never have encountered as Defence Secretary. The Soviet submariner was one; Beth, a former Greenham Common peace campaigner, another. In 1988 she ‘invaded’ Imber as part of an anti-war protest that was quasi-military in its audacity, planning and element of surprise. I didn’t have to agree with her world view to appreciate her testimony, or her sincerity.

In the end, though, it was meeting and hearing about the unsung heroes of the British defence establishment that will stick in my mind. To get back to my original point, they were solid, dependable types who, at the most basic level, turned up on time and did what they said they would do. They weren’t warmongers – indeed, they often tended towards caution – but they were enthusiastic for new approaches when it looked as if the old ones weren’t working. They had a can-do spirit. And it was that spirit that got us through, when the dark ages threatened to return.