"I do not now believe that any one of the hundreds of executions I carried out has in any way acted as a deterrent against future murder. Capital punishment, in my view, achieved nothing except revenge." He should know. Albert Pierrepoint was, by far, Britain's most prolific hangman. Between 1934 and 1956, he executed more than 400 men and women, among them Ruth Ellis, the last woman to be hanged in Britain, Derek Bentley, Lord Haw-Haw (the wartime traitor William Joyce) and John George Haigh, the acid bath murderer. He put to death Timothy Evans, wrongly convicted of murdering his daughter, and subsequently John Christie, the real killer. He hanged large numbers of Nazi war criminals convicted at the Nuremberg trials, including Josef Kramer, the Beast of Belsen, and Irma Grese, the cruellest woman concentration camp guard of them all. These two were among 13 he executed on the same day.

The man behind the noose, doing the job that his father and his uncle had performed before him, believed, in his own words, "that I was chosen by a higher power for the task which I took up, that I was put on this earth especially to do it". He did it better, quicker and more humanely than anyone had done before. But being an executioner (the word hangman is considered vulgar, and never used officially) is by its nature an occasional job. Pierrepoint spent the rest of his working life first as a horse-drayman delivering groceries, and then, after the war, as the genial and gregarious host of a pub he had bought near Manchester, called - the irony was not lost on him - Help the Poor Struggler. His geniality, though, never went as far as discussing his other, freelance, activity.

In his autobiography Executioner: Pierrepoint, and as brilliantly portrayed by Timothy Spall in the upcoming film, Pierrepoint emerges as a complex, enigmatic figure who, to anyone unaware of his calling, would have seemed the epitome of ordinary. He was no monster; there is no evidence of any sadistic streak or other psychological quirk suggesting that he took pleasure from what he did. At no stage does he admit to enjoying his job. He hated talking about it, and never boasted or told stories of his hanging achievements. He abhorred newspaper publicity and was genuinely distressed when his postwar activities in Germany attracted reporters to his door. Astonishingly, for many years he had not even told his wife Anne of his part-time job, making up excuses for his occasional overnight absences. Only when he had to be away for several days, in Germany, did he confess to her. By this time she had already found out, and was pleased that he had finally told her, but his work was never the subject of marital conversation. His autobiography is dedicated: "To Anne my wife who, in 40 years never asked a question... with grateful thanks for her loyalty and discretion."

Pierrepoint was proud that he had never made his own views public on the rights and wrongs of the death penalty. When he appeared before the 1949 Royal Commission on the subject he was asked: "Have you had any experience of judging what the general opinion of ordinary people in England is about capital punishment? I imagine people talk to you about your duties?" His reply: "Yes, but I refuse to speak about it. It is something I think should be secret. It is something I think should be sacred to me, really." His use of the word sacred is telling. His was a calling, not a trade or profession, and Pierrepoint regarded it religiously. He wrote about his hanging duties as a priest would do.

"A condemned prisoner is entrusted to me, after decisions have been made which I cannot alter. He is a man, she is a woman who, the church says, still merits some mercy. The supreme mercy I can extend to them is to give them and sustain in them their dignity in dying and in death. The gentleness must remain." He would not tolerate anyone making macabre or lewd remarks or jokes about the body, and never did so himself, even in the convivial atmosphere of his pub.

When his autobiography was published in 1974, it was the first time he had made his views on capital punishment public - a decade after its abolition. "If death were a deterrent, I might be expected to know. It is I who have faced them last, young men and girls, working men, grandmothers. I have been amazed to see the courage with which they take that walk into the unknown. It did not deter them then, and it had not deterred them when they committed what they were convicted for. All the men and women whom I have faced at that final moment convince me that in what I have done I have not prevented a single murder. And if death does not work to deter one person, it should not be held to deter any."

Yet there is nothing he ever wrote suggesting that he felt any regret or remorse at the central role he had played; nor any explanation of why and when he had reached that startling conclusion. There are no indications that he found it morally difficult to try to reconcile his feelings about the efficacy of hanging with the job he did with such pride. He was capable of analysing his own contribution in a vacuum, divorced from the national debate on the larger issue. Perhaps he only discovered his intellectual objections to the death penalty long after he had ceased being the hangman; he does not tell us.

If Pierrepoint felt any strong emotions about the people he executed, he did not admit to it. He showed no signs of being affected by, or indeed interested in, the details of the crimes committed by those whose lives he was to end; he seemed untouched by knowing that some of the men he had executed had been innocent - Timothy Evans, for instance. Others may have made a mistake; it was not his concern. Even when Pierrepoint tells the story of having to execute someone he knew - a regular customer and his singing partner at the pub, who had killed his girlfriend in a jealous frenzy - he expresses no particular sorrow, only satisfaction that he had made the condemned man's last few minutes more bearable by addressing him as a friend, by his nickname, Tish.

Pierrepoint never publicly revealed his reasons for resigning as chief executioner, but it was not, as has been rumoured, because he had become opposed to capital punishment or revolted by the act of hanging. At no stage of his career was he troubled by his conscience, and the fact that he didn't believe in the death penalty as a deterrent had no bearing on his willingness to do his job.

Nor, as another rumour suggested, was it a reaction to having to hang Ruth Ellis. "At the execution of Ruth Ellis no untoward incident happened which in any way appalled me or anyone else, and the execution had no connection with my resignation seven months later. Nor did I leave the list [of executioners], as one newspaper said, by being arbitrarily taken off it, to shut my mouth, because I was about to reveal the last words of Ruth Ellis. She never spoke." (Pierrepoint had told the Royal Commission years before that, in the moments before execution, "I think a woman is braver than a man... I have never seen a man braver than a woman.").

The truth behind his resignation is more prosaic. He had travelled to Strangeways to execute a prisoner who, at the last minute, received a reprieve. The prison refused to pay the fee for his wasted journey. His pride hurt, he chose to resign rather than accept the paltry sum offered. He was only 51, and spent most of his remaining years in Southport, running or working in pubs, discreet until the end. He died in 1992, aged 87.

Neither was he, contrary to widespread belief, Britain's last hangman. After his sudden resignation there were 37 further executions before the abolition of the death penalty. The last two were carried out at exactly the same time in Liverpool and Manchester, on August 13 1964, so that neither executioner could claim to have individually performed the last one. The whole passionate debate over capital punishment had taken place without a word from the man who knew more about it than any one alive.

· Pierrepoint is released on April 7.