It may have taken longer to make than it took to win World War II, but a new film about code-breakers at Bletchley Park finally opens at the Edinburgh Film Festival on Saturday.

It has taken six years to turn Robert Harris's best-selling book Enigma into a film, which chronicles British attempts to crack the Nazi Enigma Code - the backbone of German military and intelligence communication.

Scott: Inaccurate films are "insulting"

The film was produced by Mick Jagger, and stars Kate Winslet and Dougray Scott, who plays a brilliant young code-breaker.

Scott immersed himself in the history of the period because he wanted the film to be as authentic as possible.

"Historical films are very difficult to get right," he says.

"If you change history to make your film then that is fine, but not when it involves people's lives and the bravery of people. I think that's kind of insulting.

"The need to get this right was in homage to the people at Bletchley Park who did so much to help win the Second World War."

In fact, some say their code-breaking efforts helped shorten the war by at least two years.

It's important that we try... to give an accurate representation of what happened Robert Harris Enigma author

But have the film makers got it right?

"It couldn't be historically accurate because, to be historically accurate, you'd had to have worked there," was the first response of the Honourable Sarah Baring who, as Sarah Norton, worked as a translator at Bletchley Park.

"I thought the canteen was much nicer than ours was.

"But I thought it was a wonderful film, with great action," she adds.

Code-breaking may have shortened the war

"The film illustrates so well the aura of excitement when codes are broken and the deep depression when they temporarily cannot be cracked."

The release of Enigma comes after Hollywood stands accused of re-writing history.

Films like Saving Private Ryan and U-571 overlook the British contribution to the war and make the Americans the heroes. There is even talk of an American version of the escape from Colditz.

Robert Harris, who worked closely with the makers of Enigma, says he hopes the film will set the record straight.

"It's important that we try, as far as we can, to give an accurate representation of what happened," he says.

Harris: Wrote original Enigma novel

"Because for many people, especially children, this is going to be their main contact with the historical period.

"If you get it wrong, if you do what the Americans increasingly do and make the war completely American-centric, and have ludicrous errors, then I think that is a disservice to history by the most powerful medium of the age."

But for some, the disservice comes from making the movie in the first place.

Not everyone who worked at Bletchley Park is happy about the film.

Bobby Osbourne, now Lady Bobby Hooper, worked in Hut Eight - which was the Enigma Hut - for four years and did not like Robert Harris's book.

Kate Winslet also stars in the film

"It bore no relation to the Bletchley Park I knew and worked at," she says.

And she will not be going to see the film.

Sixty years after the British cracked the Enigma code, she can see only pitfalls in fictional films inspired by real events.

"I think it trivialises it. It's a way of making money. It's a way of entertaining people. I don't particularly care for it, but I'm only one.

"Plenty of people have read the book, and plenty of people will go to see the film."