Film starring Benedict Cumberbatch and Keira Knightley accused of romanticizing pioneering scientist's life

Alan Turing's niece Inagh Payne has questioned the accuracy of The Imitation Game, the forthcoming biopic of her uncle, the codebreaker and pioneering computer scientist, starring Benedict Cumberbatch.

Speaking to the Mail on Sunday, Payne particularly expressed concern over the casting of Keira Knightley as parson's daughter Joan Clarke, who worked at Bletchley Park with Turing and was briefly engaged to him.

'Joan Clarke was rather plain,' Payne said. "But she was very nice, bright and a good friend to Alan... When he told her about how he was she accepted it, didn't make a scene or anything like that."

"I think they might be trying to romanticise it. It makes me a bit mad. You want the film to show it as it was, not a lot of nonsense."

Turing worked at Bletchy Park as a codebreaker during the second world war, before joining the National Physical Laboratory, where he designed the early computer ACE, and then Manchester University's Computing Laboratory. Turing was convicted of gross indecency in 1952, and accepted "chemical castration" - hormone treatment – to avoid imprisonment. He killed himself two years later, in 1954.

In 2009, prime minster Gordon Brown issued an apology on behalf of the government for its treatment of Turing, and parliament agreed to pass a bill giving him a posthumous pardon.

The Imitation Game, directed by Headhunters' Morten Tyldum is due for release next year.

• Benedict Cumberbatch to play Alan Turing in The Imitation Game• Ben Summerskill: Pardoning Alan Turing is a pointless exercise © Guardian News and Media 2013