This is a piece that John Rettie wrote for the Observer in 2006, recalling the Kruschev story mentioned above:

The secret speech that changed world history
Fifty years ago Nikita Khrushchev shocked the Soviet Union by denouncing Stalin in a special address to Communist party comrades. The text, detailing the dictator's crimes, was smuggled out of Moscow and later published in full in The Observer. John Rettie recalls his part in the mission and reflects on a pivotal episode of the 20th century:

The sublime strains of Sibelius echoed off the walls of my Moscow flat as Kostya Orlov unfolded Nikita Khrushchev's grim tale of the obscene crimes committed by his predecessor, Josef Stalin. It was an evening half a century ago, a week or so after Khrushchev had denounced the horrors of Stalin's rule to a secret session of the Soviet Communist Party's 20th Congress.

That was only three years after the death of Stalin, mourned by the great majority of Soviet citizens, who saw him as a divine father. So soon afterwards, here was their new leader telling them they had made a cataclysmic error: far from divine, Stalin was satanic. The leaders who inherited the party from the old dictator agreed that Khrushchev should make the speech only after months of furious argument - and subject to the compromise that it should never be published.

Its consequences, by no means fully foreseen by Khrushchev, shook the Soviet Union to the core, but even more so its communist allies, notably in central Europe. Forces were unleashed that eventually changed the course of history. But at the time, the impact on the delegates was more immediate. Soviet sources now say some were so convulsed as they listened that they suffered heart attacks; others committed suicide afterwards.

But when Kostya Orlov, a Russian contact I now suspect was working for the KGB, phoned me that evening in early March 1956, I knew little of all this. For the 10 days of the congress, the handful of Western correspondents in Moscow had read speeches that roundly condemned 'the cult of personality', a well-understood code meaning Stalin. The party's Central Committee building hummed with activity on the night of 24 February, its windows blazing with light well into the small hours. But why, we wondered, was this going on after the congress had formally closed? It was only years afterwards that it became clear that the party leadership was still arguing about the text of the speech to be made by Khrushchev the next morning to a secret session of party delegates.

In the next few days diplomats of central European communist states began to whisper that Khrushchev had denounced Stalin at a secret session. No details were forthcoming. I was working as the second Reuters correspondent in Moscow to Sidney Weiland, who - more for form's sake than anything - tried to cable a brief report of this bald fact to London. As expected, the censors suppressed it.

Then, the evening before I was due to go on holiday to Stockholm, Orlov telephoned to say: 'I've got to see you before you go.' Hearing the urgency in his voice, I told him to come round at once. As soon as he said why he had come, I deemed it wise to confuse the microphones we all thought we had in our walls by putting on the loudest record I had. So, through soaring trombones, Orlov gave me a detailed account of Khrushchev's indictment: that Stalin was a tyrant, a murderer and torturer of party members.

Orlov had no notes, far less a text of the speech. He told me that the party throughout the Soviet Union heard of it at special meetings of members in factories, farms, offices and universities, when it was read to them once, but only once. At such meetings in Georgia, where Stalin was born, members were outraged at the denigration by a Russian of their own national hero. Some people were killed in the ensuing riots and, according to Orlov, trains arrived in Moscow from Tbilisi with their windows smashed.

But could I believe him? His story fitted in with what little we knew, but the details he had given me were so breathtaking as to be scarcely credible. It is easy now to think that everyone knew Stalin was a tyrant, but at that time only an unlucky minority in the USSR believed it. And to accept that Khrushchev had spoken of this openly, if not exactly publicly, seemed to need some corroboration - and that was not available.

There was another problem, too. 'If you don't get this out, you're govno [shit],' he told me. That sounded like a clear challenge to break the censorship - something no journalist had done since the 1930s, when Western correspondents would often fly to Riga, capital of the still independent Latvia, to file their stories and return unscathed to Moscow. But Stalin had ruled with increasing severity for two more decades since then, and no one would have risked it in the 1950s.

Feeling unable to resolve this problem on my own, I called Weiland and arranged to meet him in the centre of town. It was intensely cold, but we stayed outside where there were no microphones. Thick snow lay on the ground but we tramped through it, pausing only now and then for me to consult my notes under the streetlamps. We noted that Orlov had often given me scraps of information that had always proved correct, though not of major importance. His story fitted with the limited reports circulating in the Western community. And we noted that a temporary New York Times correspondent was leaving the next day and would certainly write about these reports. So we could be beaten on our own, far better, story. We decided we had to believe Orlov.

Next morning, I flew to Stockholm from where I called Reuters' news editor in London. My name, I insisted, must not appear on either story, and they should both have datelines other than Moscow: I did not want to be accused of violating the censorship on my return to Moscow. Then, after several hours writing up my notes, I dictated the two stories over the telephone to the Reuters copytaker. Still nervously determined to conceal my identity, I assumed a ridiculous American accent. The ploy failed dismally. 'Thank you, John,' he signed off cheerfully.

Back in Moscow, everything continued as before. During that summer of 1956, Khrushchev's thaw blossomed and Muscovites relaxed a little more. But in central Europe the impact of the speech was growing. By autumn Poland was ready to explode and in Hungary an anti-communist revolution overthrew the Stalinist party and government, replacing them with the short-lived reformist Imre Nagy.

In Moscow, the Soviet leaders were thrown into turmoil. For six weeks not one appeared at any diplomatic function. When they reappeared they looked haggard and older. This was especially true of Anastas Mikoyan, Khrushchev's right-hand man, who had constantly urged him on to greater reforms. According to his son, Sergo, that was because Mikoyan had spent long days in Budapest desperately trying to save the Nagy regime, without success. In the end, the diehard conservatives won the argument, insisting that for security reasons the USSR could not let a neighbouring country leave the Warsaw Pact. Khrushchev and Mikoyan reluctantly agreed it should be crushed .

In the West, the impact of the speech received a colossal boost from the publication of the full, albeit sanitised, text in The Observer and the New York Times. This was the first time the full text had been available for public scrutiny anywhere in the world. Even local party secretaries who read it to members had to return their texts within 36 hours. (Those texts were also sanitised, omitting two incidents in the speech that Orlov related to me.)

According to William Taubman, in his masterly biography of Khrushchev, the full text leaked out through Poland where, like other central European communist allies, Moscow had sent an edited copy for distribution to the Polish party. In Warsaw, he said, printers took it upon themselves to print many thousand more copies than were authorised, and one fell into the hands of Israeli intelligence, who passed it to the CIA in April. Some weeks later the CIA gave it to the New York Times and, apparently, to The Observer's distinguished Kremlinologist, Edward Crankshaw.

Exactly how he obtained it is not recorded. But on Thursday, 7 June, at a small editorial lunch traditionally held every week in the Waldorf Hotel, Crankshaw 'modestly mentioned that he had obtained complete transcripts of Khrushchev's speech', according to Kenneth Obank, the managing editor. The meeting was galvanised. Such a scoop could not be passed over and, with strong support from David Astor, the editor, as well as Obank, it was agreed that the full 26,000 words must be published in the following Sunday's paper.

This was a heroic decision bordering, it seemed, on folly. In those days everything had to be set in hot metal to be made up into pages. By that Thursday, according to Obank, 'half the paper had been set, corrected and was being made up. Worse, we found that we would have to hold out almost all the regular features - book reviews, arts, fashion, bridge, chess, leader-page articles, the lot. The Khrushchev copy, page by page, began flowing. As we began making up pages, it became clear that still more space would be needed, so we gulped and turned to the sacred cows - the advertisements.' Seven precious columns of advertising had to be discarded. An endless number of headlines, sub-headings, cross-heads and captions had to be written as the copy wound its way through the paper.

But the gamble paid off. Reader response was enthusiastic. One said: 'Sir, I am just a chargehand in a factory, hardly a place where you might expect The Observer to have a large circulation. But my copy of the Khrushchev edition has been going from hand to hand and from shop to shop in the administration offices, transport etc. I was quite amazed at the serious interest shown as a result of the very minute examination of the speech.'

The paper sold out and had to be reprinted. That, surely, was justification for the extraordinary decision to print the full text at three days' notice. 'Minute examination' greatly contributed to the thinking that eventually gave birth to reformist 'Euro-communism'.

Khrushchev was clearly shaken by developments. His opponents gained strength, and in May 1957 came within an ace of ousting him. When a majority in the Presidium of the Central Committee (the Politburo) voted to depose him, only his swift action to convene a full Central Committee meeting gave him a majority. It was his opponents, notably the veteran Vyacheslav Molotov and Lazar Kaganovich, who were deposed.

But seven years later the conservatives did succeed in ousting him. Twenty years of Leonid Brezhnev followed, during which the clock was turned back, if not to full-scale Stalinism, at least part of the way. But there were Communists who never forgot Khrushchev, and in particular his 'secret speech'. One was Mikhail Gorbachev, who had been a student at Moscow University in 1956. When he came to power in 1985 he was determined to carry on Khrushchev's work in reforming the Soviet Union and opening it to the rest of the world. More than once he publicly praised his predecessor for his courage in making the speech and pursuing the process of de-Stalinisation.

Some may doubt that Stalin's Soviet Union could ever have been reformed, but Khrushchev was not among them - and neither, indeed, was Gorbachev. But after two decades of decay under Brezhnev, even he could not hold the country together. It can well be argued that the 'secret speech' was the century's most momentous, planting the seed that eventually caused the demise of the USSR.