Actor Benedict Cumberbatch has called on the Duke and Duchess of Cambridge to act on a campaign that seeks to pardon tens of thousands of gay men prosecuted along with British codebreaker Alan Turing.

Cumberbatch, who has been nominated for an Oscar for his portrayal of Turing in The Imitation Game, wants 49,000 other men convicted for their sexuality to be pardoned like the pioneering computer scientist.

One of those men is 91-year-old George Montague:

Turing committed suicide in 1954, two years after being convicted of gross indecency for being gay.

In an open letter to the British government seeking action, campaigners call for the royal family to act and convince the government to pardon those convicted.

The letter, published in The Guardian newspaper, states: "The UK's homophobic laws made the lives of generations of gay and bi-sexual 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 a pardoning all the men, alive or deceased, who like Alan Turing, were convicted."

Stephen Fry and the gay rights campaigner Peter Tatchell have also signed the letter.

Morten Tyldum, director of The Imitation Game, Turing's niece Rachel Barnes, and Matthew Todd, editor of Attitude Magazine, are among the other signatories.

The letter continues: "Alan 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."

"Winston Churchill said Alan Turing 'made the single biggest contribution to the Allied victory in World War II'."

An "unequivocal apology" for his treatment was issued by then British Prime Minister Gordon Brown in 2009. Queen Elizabeth II gave Turing a posthumous pardon under the Royal Prerogative of Mercy in 2013.

Campaigners say this should now be extended to all of the men who fell foul of the law.

"The apology and pardon of Alan Turing are to be welcomed but ignores over 49,000 men who were convicted under the same law, many of whom took their own lives," the letter said.

"An estimated 15,000 men are believed to still be alive." A petition calling for action has been signed by more than 40,000 people.

Originally posted at 8.19am