With the 70th anniversary of the end of the Second World War, and Oscar buzz surrounding The Imitation Game - the film charting the story of Enigma codebreaker Alan Turing and his one-time fiancee Joan Clarke, there's never been a better time to bring out a book about Bletchley Park.

The movie tells how Turing deciphered messages encrypted by the German Enigma machine, which provided vital intelligence for the Allies. In 1952, however, he was prosecuted for homosexuality and accepted chemical castration rather than prison. He committed suicide in 1954, aged 41.

Now, award-winning broadcaster and historian Tessa Dunlop has chosen to focus on the women who worked at Bletchley in Buckinghamshire.

Tracking them down, though, was no easy feat, as less than 10% of the workforce of Britain's most secret enclave is still alive.

Still, with some perseverance, she managed to find 15 women who worked there during the war, and has charted their stories of war, secrecy, love and loss in her new book, The Bletchley Girls.

In the film, Oscar-nominee Benedict Cumberbatch portrays Turing - widely regarded as the father of the modern computer - as a socially-inept loner and genius mathematician, who believes he can single-handedly crack the Enigma code.

But some of his former female colleagues have different recollections.

Lady Jean Fforde worked directly for Turing in Hut 8. "He was an awfully nice man," she says, listing his personal idiosyncrasies as "shabby, knitting, nail-bitten, tieless, sometimes halting in speech and awkward of manner", a man famous for his gas masks and curious cycling habits.

His erstwhile fiancee Joan Clarke (played by Keira Knightley in the film), one of Bletchley's rare female cryptanalysts, worked with him.

"Everybody talked about their engagement," Lady Jean recalls. "They thought it was fantastic that Joan should be going around with him. She didn't know he was homosexual to begin with, and when she found out, she said, 'You knew what he was and you never told me!' She didn't know and she felt a fool."

Rozanne Colchester, now 91, arrived at Bletchley when she was 19. She spoke Italian, as her father had been an air attache in Rome during the war - she had met Hitler when he visited the British Embassy there.

"Hitler was blonder than I thought. I always imagined he'd be a sort of Charlie Chaplin figure with a black moustache. But I do remember - when I shook hands with him - his eyes, which were rather strange, rather fanatical and wild."

Before arriving at Bletchley, she recalls: "I had a briefing and was told it was a terribly secret place, and went to work for the Italian section of the RAF there.

"We were told we had to do very secret work and must never breathe a word about it, or go into other people's rooms or other huts in the park, or talk about our work. We were told that if we were found gossiping about it, we were quite likely to be shot.

"It was isolated. You weren't allowed to tell anybody what you were doing, not even your friends who were on the same job."

She knew Turing in passing: "He was very nice, very polite and always very busy and involved. He wasn't interested in girls. It wasn't known generally that he was a homosexual but we suspected, because he was always with men friends."

Within the confines of the park there was a sense of laissez-faire, Colchester recalls.

"At first, I was amazed that people were sleeping with each other and married people were having affairs. Nothing like that had ever happened before in my life. One grew up a lot there."

Bletchley girls tended to be well-educated, middle class young women with language skills, Dunlop observes.

"What we don't talk about enough in this country was that our women were more engaged in our war effort than any other country fighting in the Second World War. Over seven million British women were actively engaged in the war effort. There was no option for a girl - she had to work."

A lot of the Bletchley women weren't aware of exactly what they were doing, as far as their contribution to codebreaking was concerned. It was more of a production line, each section segregated from the next to ensure the secret remained safe.

Dunlop explains: "Very few women went to university. You were more likely to go to Bletchley Park if you had a language. They were part of a codebreaking conveyor belt.

"Each part of the process cooked up by the likes of Turing was done by different cogs. One girl was ticking a box, another was inputting a formula into a wheel, but none of them had a bigger picture. It was literally a factory for codebreaking. It was hard, monotonous work.

"These women were the work ants, the backbone. Take them away and you wouldn't have had anyone to implement the blueprint of the genius."

Colchester, who went on to have five children and now has 15 grandchildren, was there from 1942-45. It was 30 years before she found out how crucial the role of Bletchley Park had been in bringing the war to an end.

At the end of the war, she worked in Cairo for MI6 and married an SAS parachutist.

"Life was quite exciting," she recalls, chuckling.

She didn't tell her children for years, and when she was allowed to talk about it, some 30 years later, she felt tremendous relief.

Doris Moss, 92, fled Belgium with her sister to escape the Nazis during the war, settling with their uncle in Kent. Thanks to his connections, they both went to work at Bletchley.

She recalls: "We didn't have much time to do anything but our work, because we worked in shifts. I'd only been in England since 1942 and we didn't mix so well, because my sister and I were together.

"We didn't really know how important the work that we were doing was, except that we were deciphering naval messages in Italian.

"The hardest thing was the shifts. We worked evenings, nights and days - one after the other. It was exciting when you got the message out and you saw something about the Bismarck [Nazi battleships], even though you didn't understand what."

After Bletchley, Moss worked in a bank, which she admits seemed mundane in comparison. She eventually got married and had three children, and now helps out at charities, including Age Concern.

For some, leaving Bletchley proved an anticlimax, says Dunlop.

"In the Fifties, the message was to get women back into the home - there wasn't a big celebration of what women did in the war."

So, what long-term impact did Bletchley have on these women?

"For some, it's having its biggest impact now," adds Dunlop. "A lot of them didn't realise that what they were doing in the war was ground breaking.

"There aren't many women in their 90s who have gone through their life being unrecognised, who suddenly find themselves catapulted into a modern world that cares about their past."

:: The Bletchley Girls by Tessa Dunlop is published by Hodder & Stoughton, priced £20. Available now