Eleven signatories call on David Cameron to exercise his power and formally forgive the Enigma codebreaker

This article is more than 7 years old

This article is more than 7 years old

Alan Turing, the Enigma codebreaker who was convicted of homosexuality in 1952, should receive a posthumous pardon, Professor Stephen Hawking and other leading scientists have urged.

In a letter to the Daily Telegraph, Hawking, the world-renowned physicist, and 10 other signatories say David Cameron should "formally forgive" the mathematician.

The letter comes after Lord Sharkey, a Liberal Democrat peer and one of the signatories, introduced a private member's bill in the Lords to grant Turing an official pardon this summer.

Other signatories to the letter include Lord Rees, the astronomer royal, Sir Paul Nurse, the head of the Royal Society, and Lady Trumpington, who worked for Turing during the war.

Turing died from cyanide poisoning two years after being convicted of gross indecency at a time when homosexuality was still illegal. An inquest found that he had killed himself.

The cruelty of Turing's treatment, though not exceptional at the time, was made worse because it led to a course of hormone therapy, or "chemical castration".

Turing's work at Bletchley Park is widely credited with having helped speed the end of the second world war and he is increasingly acknowledged as the "father of the computer".

The letter describes Turing as "one of the most brilliant mathematicians of the modern era", and pays tribute to his "astonishing achievement" in breaking the German Enigma code.

"Yet successive governments seem incapable of forgiving his conviction for the then crime of being a homosexual," the letter continues. "We urge the prime minister to exercise his authority and formally forgive the iconic British hero."

In 2009 Gordon Brown, the then prime minister, made a posthumous apology to Turing, describing his treatment as "appalling". But he was not officially pardoned.

A previous appeal for a pardon was turned down by the Coalition in February. Lord McNally, the justice minister, said the case was "shocking" but a pardon was "not considered appropriate as Alan Turing was properly convicted of what at the time was a criminal offence".