If that is so, then the most prolific British executioner of the 20th century would have been horrified by the decapitation of Barzan al-Tikriti.

Mr Pierrepoint was meticulous in his preparation to avoid such errors, which were not uncommon before he was appointed chief hangman in 1946.

Most important was the art of judging the “drop” — the length of rope required to kill the condemned as quickly and painlessly as possible. Too long and the force of the fall would decapitate the prisoner — as happened in Baghdad — too short and it would slowly strangle him.

Mr Pierrepoint carefully recorded the height and weight of those to be executed in a series of log books. The length of drop was calculated using the 1913 Official Government Table of Drops.

However, the tables were only approximate and the hangman’s skill lay in sizing up the prisoner the night before, usually by looking through a secret observation window. On one occasion Mr Pierrepoint disguised himself as a warder to enter the cell to get a better look.

He had his own white hood to place over the head of those to be hanged, a tape to measure the drop and a hanging rope of a quality superior to that provided by the Home Office.

Mr Pierrepoint, who came from a family of executioners and learnt his trade by practising on a dummy, expected to complete the execution within eight to ten seconds of entering the execution chamber and was appalled by the traditional drink enjoyed by some hangmen before the drop and by rowdy behaviour in the execution room.

During his 25-year career, first as assistant and later chief hangman, he dispatched 433 men and 17 women. They included William Joyce, the traitor known as Lord Haw Haw, and Ruth Ellis, the last woman to be hanged in Britain. He also served as an executioner after the Nuremberg trials, hanging 200 Nazi war criminals — 27 on one day.

After resigning in 1956 Pierrepoint wrote: “Capital punishment in my view achieved nothing except revenge.”

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