Exclusive: a recording of the voice of Guy Burgess - the most colourful and notorious of the cold war spies - has come to light thanks to a freedom of information request to the FBI.

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Guy Burgess was, at various times and often simultaneously, a radio producer for the BBC, an informer for MI5, a propagandist for MI6 and a spy for the KGB, writes Stewart Purvis. In the book which I wrote with City University colleague Jeff Hulbert last year, When Reporters Cross the Line, we said that Guy Burgess set something of a gold standard for conflicts of interest.

During the research for our Burgess chapter we found all sorts of facts about the man and his extraordinary life. We knew what he looked like from stills and one piece of silent newsreel. We knew how tall he was, what he weighed, the various ailments he collected because of his prodigious drinking and who he slept with. We even found out that he smelt like a combination of the previous night's alcohol and that morning's chewed garlic cloves.

But nowhere could we find exactly what he sounded like. The BBC sound archive produced no trace of a recording of their former employee. We had a hunch that somewhere in the many radio programmes Burgess had produced, he probably had appeared on the air at some point, but maybe nobody wrote it down.

Despair over Munich

All we could find was a reference in, of all places, the FBI files in Washington, to Burgess having made a sound recording in 1951, just before he defected to Russia, in which he told his favourite anecdote. He had talked about the day back in September 1938 when he met Winston Churchill and they shared their mutual despair at the Munich agreement which Chamberlain had just signed with Hitler. The files had a transcript of what Burgess had said about this meeting into a friend's tape recorder in New York the day before he got on the boat back to Britain and then on to Russia.

The only known recording of the voice of one of Britain's biggest traitors was in excellent quality.

We thought that if a transcript existed it was obvious that at some point a tape existed and might still exist. So Jeff put in a freedom of information (FOI) request on our behalf to both the British and American authorities. The British came back saying they didn't know where any such tape was, but nine months after our request the FBI told us they had put "a release" in the transatlantic mail. It came in the Christmas post, and on our first day back after the holiday break we found an FBI envelope sitting in my post box at City University.

I was so excited that I took Jeff and the envelope into a studio at City University to record in sound and video the moment of us opening the envelope. Michael Crick of Channel 4 News, to whom we gave the tapes, was to say later that only an old newsman would think of recording the moment. We feared that the "release" might be just more paperwork, but in fact the FBI had run off a CD for us of Burgess's tape which they had discovered in New York during their inquiries after his defection to Russia. The only known recording of the voice of one of Britain's biggest traitors was in excellent quality, and alongside it was an FBI letter declaring that the tape was now declassified and released without any deletions.

Not posh enough

When we listened to the CD we realised that it contained what was the third attempt by Burgess and his friend on that slightly drunken night to put his anecdote onto tape. The very first words on the recording - which weren't on the transcript - are Burgess declaring, presumably in response to his friend giving him some kind of advice off mike: "I won't take any notice of you... I'm not in the least shy. I am extremely tired."

In some ways this is a short radio play about the meeting between Burgess and Churchill, in which Burgess plays both parts.

He then explains: "I am now recording for the third time, because I think the story is of some interest, my interview with Mr Winston Churchill in September 1938." Burgess was known as a good mimic and he imitates Churchill's side of the conversation. In some ways this is a short radio play about the meeting between Burgess and Churchill, in which Burgess plays both parts. He delivers his lines with a slight slur, which may be due to the amount of drink that he had been consuming just before finally sorting out the tape recorder.

Burgess has been played on screen half a dozen times by actors including Alan Bates, Benedict Cumberbatch and Derek Jacobi. Mostly they played the Old Etonian with what we would regard as a posh accent. But being the first people anywhere to hear the voice of the real Guy Burgess for the first time since he died in Moscow in 1963, what struck us that none of the actors had been anywhere near posh enough in their versions. The real Burgess was much closer to Harry Enfield's character Mr Cholmondley-Warner than to a contemporary old Etonian like David Cameron.

When Burgess met Churchill

Guy Burgess met Winston Churchill at an extraordinary time: the day after Neville Chamberlain had signed the Munich agreement with Hitler, allowing Nazi Germany to swallow up a significant portion of Czechoslovakia, writes TV Producer Tim Bouverie.

The British public were ecstatic. Chamberlain was a hero - the man who had pulled Europe back from the brink and secured "peace with honour". There was only a rump of Conservative and some Labour politicians who disagreed and foremost among them was Churchill. To Churchill, as to Guy Burgess, Munich was a disgrace. Britain had given in to a bullying dictator and betrayed the Czech people. Furthermore, it seemed to Churchill (and Burgess) that the craven weakness of the western democracies made war more not less likely.

This then was the context in which Guy Burgess - a BBC political journalist, Cambridge graduate and Soviet spy - drove down to Westerham to meet Winston Churchill. According to Burgess, the pair got on. They had some "mutual hatred" of Chamberlain, and Churchill was pleased when Burgess urged him to "stump the country" and waken the British people from their collective naïvety.

None of this seems improbable. Burgess, a Communist, was a fervent opponent of fascism. Churchill, the realist, saw that Hitler could not to be trusted. Nevertheless there is a great dramatic irony overhanging this fascinating recording: namely, that Winston Churchill, the great British patriot and future prime minister, was unaware that he was conversing with the man who was to become, perhaps Britain's most notorious traitor.

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'Establishment' Burgess

We have gathered together everything from our research - video, audio, documents, articles and stills - and put them on a microsite www.city.ac.uk/Burgess so that anybody inside or outside the university can use these resources. My thanks to one of the students on the broadcast journalism course, Kristian Brunt-Seymour, who has edited the video and audio and voiced the news package we have produced, to Ben Sawtell who has created the microsite with his colleagues in the City University communications team, and to Dave Goodfellow and the technical team in the journalism department who made it all work.

As a hack at heart, I get a cheap thrill of getting the exclusive which nobody else has before, but my colleague Mr Hulbert thinks rather more deeply about the historical significance of what we have found. He believes that we can now hear for ourselves exactly how "establishment" Burgess was and it helps to explain why he found it so easy to mix with the ruling elite: he spoke and sounded just like they did.

But Jeff thinks the tape also reveals Burgess's underlying sense of humour, which for many was his underlying charm, as well as a quick wit. Jeff's overall verdict is that we get a real glimpse of Burgess the man who, in spite of all his treachery, still commanded the respect and friendship of a loyal band of followers. Jeff says: "What is striking is that his voice betrays no hint of tension. This is remarkable because less than four weeks later he would defect to the Soviet Union with Donald Maclean."

Stewart Purvis is professor of television journalism at City University London and a non-executive director of Channel 4. He is also a former editor of Channel 4 News