We didn't want to get bogged down with the technicalities, nor did we want to trivialise them

Michael Apted Director

Director Michael Apted got tuition from a Cambridge maths professor so he could understand how the code machines worked, and actors were driven by Mick Jagger to Bletchley Park - now a museum - last year.

The Rolling Stones frontman's film company is behind the big screen story, adapted from Robert Harris's novel.

Although the characters are fictional, the setting is very real and work done there is said to have shortened the war by two years.

Apted says he was at pains to get the details of Bletchley Park and what went on there right - unlike some Hollywood war films that have simplified or distorted the stories.

Burrows and Scott play Bletchley code-breakers

"Trying to get a balance between the detective, thriller, human side of it, and the cerebral side of it - that was the struggle of the script," he says.

He had to "calm Stoppard down a bit" when the screenplay writer wanted to include all his intricate knowledge of how the code machines worked.

"When I read the first draft, it made my eyes water," Apted says.

"I loved it, but I didn't understand a word of it. It was terrifying."

There is a love story and a whodunit that Apted wanted to combine with the wider plot of cracking the Nazi codes.

"The whole idea... was to try to get a balance between the technicalities of it and the humanity of it," he says.

Talking to people who worked at Bletchley Park was wonderful

Dougray Scott Actor

It is rumoured that Dougray Scott read Harris's novel 10 times - as well as meeting original Bletchley workers, professors and borrowing Jagger's Enigma machine so he could work out how to use it.

"I read it a lot because it was a wonderful source of research for the character," Scott says.

His character is a brilliant but unstable Cambridge student who gets one girl (the plain Hester, played by Kate Winslet) after losing another (the glamorous Claire, played by Saffron Burrows).

"Sometimes novels are very helpful that a film is based on, sometimes they're not."

Northam: "Spiffingly over-the-top" as intelligence officer

Scott is a fast-rising star who has been tipped as the next James Bond - and he has refused to rule the possibility out.

Another of the film's strong, mainly young cast is Jeremy Northam, who plays the over-the-top British intelligence officer Wigram, who provides the film's funniest moments.

"The thing that always appealed to me about this script was that it... pits the personal crisis against the global crisis and connects the two," he says.

That makes it more relevant today than anyone involved in the film had expected - and Northam says cinema-goers may now be able to relate better to Enigma than they would have done.

Film-makers do not expect the film to hit any raw nerves after the US terror attacks - and despite hitting UK screens on 28 September, it does not open in America until February.

Ability

Kate Winslet was notable by her absence at the film's UK premi�re on Monday after dropping out following the break-up of her marriage.

But Apted praised her ability to play a character who "let the glamour to be inside her rather than outside her".

"One of the problems with the film is that it is kind of cerebral, it is kind of difficult to follow, and you need this kind of emotional area of the film to keep it alive," he says.

"Kate and Dougray brought an enormous amount to that love story."