The Imitation Game actor signs open letter calling for convictions of all 49,000 men found guilty of indecency to be wiped from the record

Benedict Cumberbatch, the star of The Imitation Game and an Oscar hopeful, has added his name to an open letter urging the British government to pardon thousands of gay men convicted of gross indecency.

Cumberbatch, who plays codebreaker Alan Turing in the Oscar-nominated biopic, has joined more than 40,000 people signing the letter to the government. The letter calls on members of the royal family to back the campaign to give a pardon to all those who were convicted of a crime because of their sexuality – a pardon that could wipe clean the records of 15,000 men still alive.

The letter states: “The UK’s homophobic laws made the lives of generations of gay and bisexual men intolerable.

“It is up to young leaders of today including the Duke and Duchess of Cambridge to acknowledge this mark on our history and not allow it to stand.

“We call upon Her Majesty’s government to begin a discussion about the possibility of pardoning all the men, alive or deceased, who like Alan Turing were convicted.”

Turing led efforts to crack the Nazi Enigma code and was hailed by Winston Churchill as the person who “made the single biggest contribution to the allied victory in World War II”.

He was convicted of gross indecency in 1952 and was chemically castrated. He took his own life in 1954. Turing was given an official apology by the British government in 2009, when the then prime minister, Gordon Brown, spoke of the “appalling treatment” he had been subjected to. Four years later, the Queen granted him an official pardon.

The letter continues: “Turing was one of the greatest heroes of the 20th century, a man whose work on the machines that deciphered the Enigma codes helped win World War II and who was pivotal in the development of modern computers.”

Other signatories to the letter include actor and broadcaster Stephen Fry, civil rights campaigner Peter Tatchell, The Imitation Game’s director, Morten Tyldum, and Rachel Barnes, who is Turing’s niece.

Turing was one of 49,000 men convicted of indecency under laws banning gay sex. He admitted in court he had formed a relationship with a friend, Arnold Murray, and was offered a choice between a prison term or undergoing a course of drug treatments aimed at controlling his libido.