Prince William and his wife Kate have declined to get involved in a campaign to pardon tens of thousands of gay men convicted alongside codebreaker Alan Turing, credited with being a key figure in winning the Second World War.

Benedict Cumberbatch, who played Turing in Imitation Game, and Stephen Fry are among campaigners who have signed an open letter asking the Prince William and his wife to support the campaign.

A spokesman for the Duke and Duchess said that as this is a matter for government they would not make any public comment.

In 2009, an "unequivocal apology" for Turing's treatment was issued by then prime minister Gordon Brown.

The Queen granted the scientist a posthumous pardon under the Royal Prerogative of Mercy in 2013, but the campaigners say this should be extended to all men who fell foul of the law.

The letter states: "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.

"An estimated 15,000 men are believed to still be alive."