"If you think Europe is having a crisis now, go back to 1946 when the entire continent was blasted back to medieval times," says Sinclair McKay, author of The Spies Of Winter, which delves into the lives of The GCHQ codebreakers, who fought the Cold War and knew the darkest secrets of British Intelligence at that time.

After World War Two had ended, the devastation left across Europe was tremendous, as hundreds of people were displaced and millions had been slaughtered.

There was also a lingering fear that the war wasn't really over and would break out again at any second. However, this time around there was also a much bigger threat as the world had moved in to the age of nuclear weapons where mass destruction was a clear and present danger.

Sinclair, who is from Limehouse in Tower Hamlets, explains why he wanted to explore the minds of those working at Bletchley Park, the central site for Britain's codebreakers during the war and shed light on the individuals who were brave enough to intercept information systems of the enemy and protect British people.

The 49-year-old says: "The post-World War Two era was the most incredibly tense time in history.

"To be at the centre of the nuclear age where at the touch of a button, generations could be killed or poisoned, it really takes a cool head and so the work of codebreakers is so admirable.

"They were intercepting messages and communications from Soviet tanks and even movements in the north of Iran, so were monitoring the whole world and how they did that without having a nervous breakdown, I really do not know.

"I was fascinated about what life was actually like at Bletchley Park for the codebreakers and how they managed to smash the Enigma code.

"I wrote this, because I wanted very much to know how Bletchley Park – after the war – then regenerated into GCHQ in Eastcote, north London, the official site of the UK Government Communications Headquarters."

Bletchley Park produced a lot of incredibly clever codebreakers who then stayed on to fight the Cold War but Sinclair's standout cryptanalyst from the era was a woman named Joan Clarke.

He says: "The most famous of the lot is of course Alan Turing, who even has The Imitation Game film out about him.

"However, the point of my book is to show that there were many other underrated people, such as Joan Clarke, who really were unsung heroes and heroines.

"She is often presented in the media as a woman who walked in off the streets, when in actual fact she was a brilliant mathematician in her own right and was headhunted.

"In clinical terms, she broke many more codes than Alan Turing ever did and I think she was a heroine. She stayed a codebreaker until the 1970s and was really a formidable presence.

"The book tries to get into the heads of codebreakers and just finding out what their lives were like as well.

"They led these incredibly secret double lives and would walk around among their neighbours and even friends and family who had no clue what they were doing for a living."

Sinclair attended the annual reunion for veterans at the Bletchley Park Museum last Sunday, and adds it is always an emotional experience.

He says: "The atmosphere during the reunion is always poignant, as it took so many years for their achievements to be acknowledged and celebrated.

"They were living in the shadows for so long and now finally, even though they are in their 90s, we can celebrate the achievements of those who saved millions of lives during the war through their secret work."

Details: bletchleypark.org.uk

By Rachel Russell