The recent death of the notorious Soviet spy George Blake reminded me of a documentary film I made many years ago with Sean Bourke, the Irish man who was responsible for springing Blake from prison.
Bourke had been befriended by Blake when they shared a cell in Wormwood Scrubs. Blake had been a high-ranking officer in MI6 and the information that he passed on to his Soviet handlers had resulted in the deaths of many British agents in eastern Europe.
In 1961 he had been sentenced to 42 years in prison: one year, it was claimed, for every agent who had died as a result of his treachery.
Bourke, meanwhile, was serving a seven-year stretch for sending a home-made bomb to a policeman who he believed had spread rumours that he was a homosexual.
Although he was still a young man, Bourke had already spent most of his life in penal institutions in Ireland and England.
That began when he was just 12 and was sent to the infamous reform school at Daingean in Co Offaly for the crime of stealing a banana.
He told me that the three years he was held in Daingean were "a living hell", and in 2009 the Ryan Commission into Child Abuse concluded that boys sent to the school were regularly subjected to brutal floggings and sexual abuse.
Bourke said that, when he was released from Daingean, he had been given a ticket for the Liverpool boat and advised to leave Ireland.
It wasn't long before he was incarcerated again - this time in an English reformatory.
Bourke had very little formal education, but he struck me as a highly intelligent individual and he was a voracious reader.
While in Wormwood Scrubs, he had founded and edited the prison magazine New Horizon. George Blake began to write for the magazine and they became friends.
Bourke was clearly flattered by the attention that a well-educated and sophisticated man like Blake gave him.
He told me he also believed the Soviet agent had received an excessive sentence - the longest ever imposed by an English court other than life sentences - and so he decided to help him escape from prison.
After his own release from Wormwood Scrubs, Bourke made contact with two supporters of the Campaign for Nuclear Disarmament (CND) who he had met in prison and who had their own ideological reasons for wanting to help Blake escape.
The plan Bourke hatched in 1966 was deceptively simple: during the prison's weekly film show, he threw a homemade rope ladder over the perimeter wall for Blake to climb and one of the CND supporters then drove both of them to a safe house.
After a few months Bourke also arranged for Blake to be driven to East Germany in the false compartment of a camper van. From there, Blake travelled on to Moscow, where Bourke joined him a few weeks later.
Bourke was deeply hurt when it became obvious Blake had no further interest in maintaining their relationship in Moscow and, instead, regarded him as a social embarrassment.
After a year or so in Russia, Bourke decided to return to Ireland. He went to Limerick, where his family lived - one of his cousins was the actor Richard Harris.
Back in Ireland, Bourke wrote The Springing of George Blake, a vivid account of the escape and its aftermath. It was very well-written, if not totally reliable, and became a best-seller.
Alfred Hitchcock bought the film rights on two separate occasions, but, sadly, the movie was never made.
Following the book's publication, the British authorities launched extradition proceedings, but the Irish Supreme Court ruled that Bourke's actions fell within the political offences exception of Ireland's extradition laws.
Sean Bourke remained in Limerick for the rest of his life. He became a committed supporter of the Democratic Socialist Party, but when I filmed with him he was almost penniless and in the throes of severe alcoholism.
I found him a most likeable and engaging character, though I spent much of my time trying to keep him sober - and not always successfully.
I found, on one occasion, that the innocuous bowl of soup he was eating for lunch had been liberally laced with vodka.
He remained extremely bitter about Blake and said he deeply regretted his role in helping him to escape.
Not long after I filmed with him, in 1982, Bourke died of a heart attack that was probably related to his alcoholism.
Since then, various conspiracy theories about his death have emerged. According to one, this was the long-term effect of poison administered by the KGB soon after he left Moscow.
According to another, he was murdered by the KGB on the orders of Blake, who apparently disliked what Bourke had written about him in his book. Neither of those theories seem plausible.
There is one final twist in this story. The English playwright Simon Grey later wrote a drama about Blake's escape and Bourke's time in Moscow called Cell Mates. The part of Blake was played by Stephen Fry and that of Bourke by the late Rik Mayall.
The production achieved notoriety when Fry disappeared just before the play was about to open in London. It transpired he had bolted to France because of an unfavourable preview notice.
Shortly before Blake died, he expressed some regret for the deaths of the agents he betrayed. But he did not mention Bourke - the man who had organised his escape from a British prison.
Neither did he apologise for his actions as a spy, claiming he had been operating on the side of "good against evil".
After his death, at the age of 98, on Boxing Day, Vladimir Putin expressed his "deep condolences" and praised "Colonel Blake's invaluable role" in "maintaining peace on this planet".