Set in the early 1950s, ITV1’s new three-part crime drama The Bletchley Circle centres on four wartime code-breakers (from left, Rachael Stirling, Anna Maxwell Martin, Sophie Rundle and Julie Graham) who use skills developed at Bletchley Park to solve a string of murders but have to conceal their past.

Here, we meet four former Bletchley girls who reveal the code-breaking they did during the war, and the lives they've led since... 

Mavis Batey, 91 – “Nothing is impossible”

When war broke out, I was writing a thesis on the German Romantics at the University of London. I thought I really ought to be doing something better than that for the war effort, so I said I’d train as a nurse, but my professor knew all about Bletchley and advised me to apply to the Foreign Office. I was sent to Bletchley in April 1940, working on German secret-service codes.

We didn’t know what it was that we were trying to break into, but we were very aware that lives were at stake. The message “jumbo rush” would mean, “Don’t stop until mission is accomplished”.

It was an extraordinary community at Bletchley, a blending of all the talents. My husband [celebrated cryptanalyst Keith Batey] was a Cambridge mathematician, my boss was a classical scholar. I suppose the “melting pot” was what made it so successful.

After the war, I worked as a landscape historian, which, it has been pointed out, involved the same sort of puzzle-solving skills finding patterns in “observables”. There are other legacies. Our motto was “nothing is impossible”. These things stay with you.

Beryl Middleton, 87 – “At first we made sandwiches”

I don’t think I’d even heard of Bletchley when I first went there. When I arrived, with a group of Wrens, it was Christmas Eve and I don’t think they really knew what to do with us, because they put us to work making sandwiches. But first we had to sign the Official Secrets Act.

The next day, nobody seemed to notice it was Christmas. I was taken to Hut Seven and put to work on Japanese codes. We were given blocks of letters, which we had to transpose onto crib sheets to look for “pattern repeats”.

One of the people who used to come into our room was a young man called Harry. We married in 1946 and I later learnt that he was one of the top code-breakers; at the time, however, the only thing I knew was that I had married a man I worked with at Bletchley. It sounds glamorous but, for all I knew, he might have been a spy.

After the war, Harry’s work for GCHQ took us to Canada and the US. Then we settled in Cheltenham. I worked part time for UCCA (the Universities Central Council on Admissions) and I was made a magistrate, where I suppose the old qualities of discretion came in.

I feel my time at Bletchley made me that bit more willing to get involved in other things. Looking back, I was very lucky. I can’t say it was exciting, exactly – at least not for those of us doing the donkey work – but you knew you were making a difference.

Nina Horwood, 88 – “The Germans were foolish”

I had taken a job with the inland revenue immediately after school. I hadn’t been there more than a week when I was called out to speak to someone from Bletchley. I suppose they asked our headmasters about what we had done at school and I had done an extra year of German.

I landed in a room where we read through German “traffic”: the blocks of signals. The Germans were fool enough to put out a weather forecast twice a day in exactly the same format. This became a daily crib for the people working on Enigma.

Social life at Bletchley was quite fun. There were clubs - drama, bridge, chess - and there was a beer tent where you could sit down with your sandwiches and meet people. But you never said what you were working on.

My husband was head of the room I worked in, but it was only after the war that we started going out. Later, we were posted to Singapore, where he died. I went back for a couple of years to GCHQ in Cheltenham and married another GCHQ person.

I don’t think my experience at Bletchley carried through to later life. When you left, you see, you never got references. They could say, “Well, she worked and she was honest,” but they couldn’t say what you had been doing. So you forgot about it all very soon and got on with the rest of your life.

Jean Valentine, 88 – “My parents never knew what I did”

I joined the Wrens when I was 18. I have never been sure, but I think I was recruited to Bletchley because I said on my application form that I enjoyed doing crossword puzzles.

I operated one of the Bombe machines [used to help decipher messages encrypted by German Enigma machines]. It was women only working on the Bombe, and at times we would work 16 hours a day. When we first started we got 15 shillings a week – now about 75p – and then, when we were proficient, it went up to about a pound. Even in those days, that was not good money!

The moment you finished work, you went back to your billet – I lived in a requisitioned house about five miles away from Bletchley, but I can’t tell you exactly where, because all the signposts had been removed for security.

Later in the war I was posted to Ceylon, now Sri Lanka, where I worked in an office breaking Japanese code – no machines to help this time – and I met my husband there. When we returned to England, I worked in Selfridges – £5 a week! – and, later, with the Family Planning Association.

I never talked about my war work. My parents never knew what I did. And neither did my husband until around 1975, when all the stuff about Bletchley started coming out.

It seems peculiar now, but it was a different climate then. Our backs were to the wall and there was discipline. It’s a word that seems to have fallen out of the English language, but in those days, if you were told not to do something, you just didn’t do it.

The Bletchley Circle starts tonight on ITV1 at 9:00pm