In the early morning hours of 25 February 1956, Khrushchev addressed a closed session (limited to Soviet delegates) of the 20th Party Congress. It became known as his ‘Secret Speech’, though news of it leaked out quickly and spread like wildfire.

Congress sat in stunned silence for four hours, as Khrushchev condemned Joseph Stalin and all his works. The speech vilified Stalin for his murderous brutality, intolerance, repression of Soviet peoples, abuse of power, the persecution of millions of innocents, and much more. In one of its most striking passages, he said:

Stalin originated the concept ‘enemy of the people’. This term automatically made it unnecessary that the ideological errors of a man or men engaged in a controversy be proven. It made possible the use of the cruellest repression, violating all norms of revolutionary legality, against anyone who in any way disagreed with Stalin, against those who were only suspected of hostile intent, against those who had bad reputations.

It was an incredibly brave speech to deliver, not only because all senior members of the Communist Party, the very highest group that composed his audience, still professed allegiance to Stalinism, but because he, himself, was a product of it. Khrushchev had, as his daughter once put it, ‘risen to power on the crest of the Stalinist wave’. He had himself implemented some of Stalin’s cruellest policies with apparent relish, most notoriously when working with Ivan Serov in the Ukraine from 1939 to 1941. Admitting his own, and the party’s, history of error took great moral courage, and brought huge political risk.

Khrushchev had not always been a devout supporter of Stalin – in the early 1920s he supported Trotsky against Stalin over the question of party democracy – and now he was openly challenging the basic concepts of Stalinism at the highest levels of the party.

The gamble paid off: most party members threw their hats into the ring with Khrushchev, who held power for another eight years, until his ousting by Leonid Brezhnev and Alexander Shelepin in October 1964. It is now widely accepted that the Secret Speech and Khrushchev’s traducement of Stalin were seeds that would germinate, in time, into the liberal reforms of Mikhail Gorbachev. Eventually, their spread across the nations of the USSR and Eastern Europe would culminate in the disintegration of the Soviet Union and reunification of a wholly capitalist Germany.

Serov was never a political animal. He possessed neither the ability nor the will required to hold one of the top party offices. His appointment as KGB chairman came about solely owing to the recommendation of Khrushchev to the Politburo – the ultimate Soviet authority. It left him subordinate to overall Politburo control, and his office did not bring him membership in the Politburo.

It is possible that Khrushchev had warned Serov of his plans to recant his previous support of Stalin, but Serov was still shocked and angered by the severity and manner of the denunciation. He would have joined any organised group strong enough to oust Khrushchev, had there been one.

The majority of Politburo members gave overt – though in some cases uncomfortable – support to Khrushchev’s new anti-Stalinist strategy, and Serov was subservient to the Politburo. This would have left a lesser operator impotent, but Serov had the conviction, strength and determination to continue promoting his own brand of Stalinist action and discipline in the KGB’s activities, regardless of the Politburo’s dictat. From this point onwards there was a discernible cooling of the close relationship between Khrushchev and Serov.

At the beginning of April 1956, just a few weeks after the Secret Speech, Serov left for the United Kingdom as the advance man for arranging security on a nine-day goodwill visit by First Secretary Khrushchev and Premier Marshal Bulganin. Stalin himself could not have created a worse impression than Serov in his most officious mode.

A senior British police officer who was coordinating arrangements for the visit said: ‘It was totally impossible to deal with him. He ranted and raved and demanded the impossible everywhere we went. On one occasion he shouted instructions to the Soviet Ambassador and the Ambassador felt obliged to accede to his demands.’

The British media branded Serov ‘Ivan the Terrible’ and ‘The Butcher’. The Foreign Office requested that Serov not return to the United Kingdom for the goodwill visit itself. No political animal, Serov clearly had his limits as a diplomat, as well.

Khrushchev and Bulganin arrived in the UK on 18 April on the prestigious new cruiser Ordzhenikidze, which docked at Portsmouth together with an escort of two Soviet warships.

The day after the boat came into harbour, the officer on watch reported seeing what appeared to be a diver under the water near the cruiser. The ship’s commanding officer consulted the senior KGB officer on board, who just happened to be Ivan Serov – who had in fact returned to the UK with the General Secretary and Prime Minister, though he did not venture ashore. He was at hand for exactly such eventualities as this, and dealt with the potential security issue simply by ordering the immediate execution of the diver.

Serov’s suspicions were correct: the diver was none other than the heroic Commander Lionel ‘Buster’ Crabb, at that time in the employ of MI6. He had been sent to inspect and photograph the Soviet cruiser’s hull and propellers, with the particular aim of investigating how the ship, given its impressive size, had proven so remarkably manoeuvrable.

Khrushchev was furious upon learning of the incident. He was furious both that Britain had dared to perpetrate such an act during a goodwill visit, and appalled that the diver had been summarily executed rather than captured. A captured spy, after all, could prove a useful bargaining chip.

However, Khrushchev was enjoying his visit – his first official visit to a Western country – and decided not to embarrass his hosts in public. He and Bulganin took British Prime Minister Sir Anthony Eden aside at a reception to register their protest. Eden was horrified. He apologised profusely and, with unfeigned sincerity, told his guests he had given no instructions to spy on the Soviet vessels. He promised to discover who had authorised the deed and take the strongest possible disciplinary action against him.

Crabb’s disappearance – initially there was no body and no evidence that a diver had died, let alone been murdered – made front page news. However, there were so many different stories and theories about the incident that it cast only a small shadow over the visit. The Times came closest to the truth with its coverage of the event, but – strongly identified with and supportive of Eden’s Conservative Party – the newspaper mysteriously backed away from the story the next day. There was certainly a successful exercise in damage limitation that lasted until after the Soviet visitors had departed.

It was almost a year later that a body in a frogman suit was found floating near Pilsey Island in Chichester Harbour. The head and both hands were missing, making identification impossible using the technology of the time, but the coroner was satisfied that it was the body of Crabb. Rumours that Crabb lived on, becoming a Soviet secret agent or possibly a double agent, still persist.

As a direct result of this incident, Eden forced Major-General John Sinclair, the Director-General of MI6 to resign, replacing him with Sir Dick White, previously the Director-General of MI5.

Just three days after the diving incident, on 22 April, another near-disaster came close to scuppering the ‘goodwill’ visit. This time, Serov was responsible.

Serov had never approved of allowing the West’s Berlin tunnel continued operation. His Stalinist instinct was to take immediate action to terminate any espionage activity as soon as it was discovered, but Sergei Kondrashev – now back in Moscow after being Blake’s spymaster in London – prevailed upon him to allow the cable-tapping to continue, in order to protect Blake’s identity as a double agent.

Conditions towards the end of April were right for the fortuitous ‘discovery’ of the tunnel and Serov gave instructions to proceed. Someone – it may have been Kondrashev – suggested that, in the light of the goodwill visit by Bulganin and Khrushchev, all of the blame for the tunnel should be placed on the Americans and none on the British. This saved the day – and the face of Her Majesty’s government.

In spite of the two near-disasters, Khrushchev and Bulganin enjoyed their nine days in the United Kingdom. The highlights for Khrushchev in particular were the incredible performance of Margot Fonteyn in a ballet at Covent Garden, and the visit to Edinburgh. He was overwhelmed with the rugged beauty and history of Edinburgh Castle, and so taken with the library in Edinburgh University that he arranged for the chief librarian to go to Moscow for six months and set up something similar in the Moscow State University library.

As goodwill visits go, it had been a civilised diplomatic success. Talks were ‘constructive’. The resulting joint communiqué pledged both nations to seek peace in the Middle East through the United Nations, to give guarantees not to use nuclear weapons, to reach agreement on disarmament, to make a significant increase in cultural exchanges, and to record a Soviet ‘aim’ to spend £1,000 million on British goods and services over the next five years. Eden accepted an invitation from Bulganin to visit the Soviet Union and publicly thanked Bulganin and Khrushchev for their ‘patience and perseverance’ during their stay in Britain.

The most unsavoury parts of the visit, according to later writings and reports, were obligatory meetings with leading members of Britain’s opposition Labour Party. The uncouth, heavy-drinking George Brown, a future deputy leader of the party and Foreign Secretary, was particularly obnoxious.

The afterglow of the visit soon faded as the Suez Canal crisis developed through the summer and into the autumn of 1956, when the Soviet Union sided with and assisted Egypt against Britain, France and Israel. In the end, it was the non-participation and veiled criticism of the United States, rather than Soviet support for Egypt, that caused France and Britain to back down.