The BBC Radio 4 transmission of the Soviet spy Kim Philby's hour-long 1981 lecture to the East German Intelligence Service, the Stasi – recently discovered in Stasi archives – has understandingly excited considerable media interest worldwide.

It is not the only film that exists of Philby speaking a similar one to KGB recruits has been known about by spy buffs for some time and Philby's press conference in 1955 denying being The Third Man is well-known – but it is the first opportunity to hear the man himself talk about his career as a Soviet agent, how he was recruited and how he operated.

What seems most incredible in his lecture is how lax document security was – he claims he simply befriended the MI6 archivist who happily showed him files he was not entitled to see and how he smuggled them out of the building to his Russian handlers.

"Every evening I left the office with a big briefcase full of reports which I had written myself, full of files taken out of the actual documents, out of the actual archives," he said.

"I was to hand them to my Soviet contact in the evening. The next morning I would get the file back, the contents having been photographed, and take them back early in the morning and put the files back in their place. That I did regularly, year in, year out."

What we have to remember is that in the 1940s, there had been no Cambridge Spy scandal. It was assumed that men from his privileged background – and most of those working in MI6 were from such backgrounds – were absolutely trustworthy. One of the greatest consequences of Philby's treachery was to reveal that such certainties could no longer hold.

The lecture took place during his only visit to the GDR – he had a prejudice against Germany dating back to his wartime experiences – at the invitation of the legendary East German spy master Marcus Wolf. By 1981 the Russians had realised how useful Philby could be – not least for inspiring new recruits and preparing young KGB officers due to be sent to English-speaking countries – and Philby was occasionally brought out to address intelligence courses. Philby, a vain man, enjoyed the attention and the fact he was treated with respect and admiration.

How different from his first few years in Russia after his defection in January 1963. Rather than being treated as the superspy he saw himself as, the Russians had been suspicious of him, regarding him as just another burnt out agent and even concerned he might be a triple agent.

He had initially found it hard to adjust to life in the Soviet Union, where he had little to do except drink, was deeply depressed and attempted suicide. His third wife Eleanor Pope Brewer, who had left her husband for him in Beirut, had joined him in September 1963 but left for the US after 15 months when she discovered his affair with Donald Maclean's wife, Melinda. Even after marriage to his fourth wife Rufina in 1971, he continued to drink heavily.

All changed in 1975 when a young KGB officer working for the Third Department, which dealt with the United Kingdom, Australia, New Zealand and Scandinavia, Michael Lyubimov, suggested Philby be used 'to put some life into work on the British target'.

Cold War double agent Kim Philby reveals life of betrayal in unearthed footage IBTimes UK

It was arranged that Philby would hold seminars for three or four young trainees in a safe house close to his flat, sharing his own experiences and helping prepare the men for service in English-speaking countries. The 1981 lecture was simply an extension of this mentoring role.

What is interesting, given that Philby spoke German, is that the lecture was in English and that, even after 16 years in the Soviet Union, he still speaks like an upper class Englishman. Indeed it is his posh-ness, he admits, which allowed him to spy without being discovered and know that if caught little would happen to him, partly because of his background and partly because it would be too embarrassing for MI6.

Self-delusion was very much part of the Philby psyche.

"Because I had been born into the British governing class, because I knew a lot of people of an influential standing, I knew that they would never get too tough with me," he told the Stasi. "They'd never try to beat me up or knock me around, because if they had been proved wrong afterwards, I could have made a tremendous scandal."

The fact his lecture was only for intelligence professionals and that he believed it would remain secret should not, however, deceive us into thinking he was speaking completely truthfully. His account of how the MI6 station chief in Beirut, Peter Lunn, preferred to take to the skiing slopes rather than keep an eye on him – thereby allowing him to escape – is a good story, but it's not true.

Likewise his justification for his betrayal of the agents sent to Albania in 1949 to foment a rising, which he argues could have led to an escalation that could have led to war with the Soviet Union. The truth is that if various crises, such as Hungary and Czechoslovakia, didn't lead to war, then it is unlikely covert operations against Iron Curtain countries would have.

Philby in 1955
Kim Philby at a press conference in response to his involvement with defected diplomats Burgess and McLean, in 1955 J. Wilds/Keystone/Getty Images

The fact is Philby had blood on his hands and didn't want to admit it. Self-delusion was very much part of the Philby psyche.

In the film, he stresses to the intelligence agents they should never confess to anything – it's a point he also makes in his unpublished memoirs – but it is not advice he himself followed.

When he was confronted in Beirut in 1963 by his former MI6 colleague Nicholas Elliott, he discussed an immunity deal along the lines of the one given to Anthony Blunt later that year. Philby then gave MI6 a three-page confession naming as a fellow agent one of his closest friends, Tim Milne, whose career never recovered from the false slur.

Kim Philby may come across in the film as an avuncular and unmistakeably British figure but even in this secret lecture he couldn't resist deceiving others and himself.

Andrew Lownie is the author of Stalin's Englishman: The Lives of Guy Burgess