It is Lord Asa Briggs’ 90th year and the celebrations are manifold. In May, it was birthday cake, champagne and a day-long colloquium in recognition of the academic’s outstanding contribution to history.

In June, he missed out on the Queen’s visit to Bletchley Park (where he was a wartime codebreaker – more on this later) to attend the 40th anniversary of the Open University, of which he was chancellor from 1978 to 1994.

Next month, he will be guest of honour at an event marking 50 years of the University of Sussex, which got its Royal Charter on August 16, 1961.

He’s just published a new book and is in the process of writing another. 2011, he says in that soft, Alan Bennett voice, is turning out to be a rather remarkable year.

Unsurprisingly, it has been a time of reflection for the Yorkshire-born, Lewes-based historian and in his next book he will look back on the relationships – with people and places – that have shaped him.

Bletchley Park – the subject of his latest book Secret Days – is one such place. Briggs, a Cambridge University history graduate, was recruited to the Intelligence Corps in 1942 and, a year later, joined Hut 6 at Bletchley as a codebreaker, intercepting and deciphering German Enigma codes and messages.

It is a misconception, Briggs writes, that the wartime codebreaking HQ was staffed solely by mathematicians and scientists.

The historian’s ability to get inside the minds of others – in this instance, the German military – was also highly prized. But working alongside mathematicians and scientists taught him the importance of an interdisciplinary approach in understanding the world – a lesson he would later bring to bear on the University of Sussex, whose founding shook up higher education in the 1960s. “I attached a great deal of importance to the way arts relate to science in founding Sussex,” he says, “and that was a view that undoubtedly began at Bletchley.”

The writing of the book was in itself something of a milestone. For a long time, Bletchley Park was “the Second World War’s best kept secret”, with staff banned from discussing the part they played for decades afterwards.

Briggs didn’t even tell his wife Susan the full details until the 1970s and his parents both died without knowing of their son’s involvement in work believed to have shortened the war by two to four years.

Again contrary to popular belief, Briggs says staff did not stay quiet purely because they had signed the Official Secrets Act but because they realised the security threat it posed.

But the secrecy went on too long in his opinion. He feels it was unfair that many struggled to find work when the war ended because they were unable to reveal what they had been doing for the previous few years. “It was a strange and somewhat unsatisfactory experience,” he muses. “I think people should have been allowed to at least say they were doing secret work at Bletchley and shouldn’t have been subject to such, to my mind, ludicrously tight restrictions of security.”

As a historian, Briggs also felt there was a “total irony” in being unable to record his part in a significant piece of British history. It was “an amazing experience” to then launch Secret Days at Bletchley Park earlier this year, to be “talking about secrets in a place where we couldn’t even talk much to each other during the war.”

In researching the book, which combines his own memories with critiques of other books written on Bletchley, Briggs says there was a sense of putting together a jigsaw. Bletchley wasn’t only a mystery to the public. “Some of the people who were indispensable to the breaking of messages transmitted in the German Enigma machine cipher were never even told that it was being broken nor, indeed, just what part they were playing in what for many of them was a boring routine process,” he writes.

For his part, his years at Bletchley “were not the golden years of my own life, as they were for some of the men and women working there, but I never believed myself to be a cog in a wheel in any sense and while at BP I felt privileged to be helping to make history.”

Bletchley left him not only with a sheaf of memories but “changed my ways of thinking and feeling.”

Briggs came to Sussex in 1961, after working as Professor of Modern History at Leeds University for six years. It wasn’t an easy decision – his wife, particularly, was unsure about leaving Leeds, birthplace of two of their four children, to come to a brand new university on the South Coast.

But Briggs remembers the moment it was decided. “We were going to Australia by boat in 1960 and about ten minutes before it was due to leave, I said to Susan, ‘I don’t think I can go without having made up my mind about this, shall I get out and call (vicechancellor) John Fulton and tell him we’ll go?’ I got out and nearly missed the boat as a consequence.”

He was the first academic to be appointed to the university, serving as Professor of History, Dean of the School of Social Studies, Pro-Vice Chancellor and, from 1967 to 1976, Vice- Chancellor. “Sussex at that time was a very exciting place,”

he recalls. “It was a rare privilege to be involved in starting a university and I had a tremendous amount of input into the curriculum and the way we handled our affairs.”

The university quickly developed a reputation for radicalism and Briggs often found himself at the centre of some very heated situations.

But he got on well with students – “Some of the so-called ‘revolting students’ are friends of mine now” – and says he never lost sleep as a result of the unrest.

“As a supervisor, his comments were invariably stimulating, reflecting his endless curiosity and extraordinary range of interests and insights,” recalled Eileen Yeo, Briggs’ first DPhil student, at a university event held in his honour in May. “But what was as striking was his approachability, his genuine interest in what every person had to say and his kindness.”

He left the University of Sussex in 1991 but Briggs retains a great interest in what happens there. “I talk to the Vice-Chancellor and know more or less what is going on.

I watch what happens with Sussex with as much interest as if I was still there.”

He has recently watched history repeat itself as the current crop of undergraduates demonstrate against issues from increased tuition fees to staff cuts. “I think it’s a very difficult time indeed for students now and for universities.

I believe in access to higher education and I don’t think the changes that are taking place in university policy are really very much on the right lines.

I’d prefer different ways of tackling them; I’d like to see some universities merge, some disappear possibly. But I don’t think anything should be done that stops people from families which have had no contact with universities from having the chance to go there.”

Briggs was a “scholarship boy”, the first of his family to go to university and he was delighted when, in 2001, Sussex launched scholarships in his name to commemorate his 80th birthday (they have been renewed for his 90th).

A belief in access to education also seems to have driven his involvement in the Open University. He says his work with the two institutions has given him more pleasure intellectually than all his other achievements to date. But he’s most proud of what he has written – among his considerable output, a fivevolume text on the history of broadcasting in the UK and a trilogy on the Victorian period which changed the way historians now view the 19th century.

“Despite all the complications of management I’ve been involved in, I’ve managed to write throughout, which was a great advantage to me as Vice- Chancellor of Sussex in that students knew I was writing.

No other Vice-Chancellor of any university in Britain has led that double life as a writer, a historian in my case, and an administrator.”

Incredibly, he still writes “around” 1,500 words a day.

Where does such a phenomenal drive come from? “It’s purely physiological,” he laughs. “I’ve always had plenty of energy and whatever problems there have been to deal with in life, I’ve been supported by a good family. I’ve been lucky.”

* Secret Days: Codebreaking In Bletchley Park is out now (Frontline Books, £19.99).

* For more information on the University of Sussex’s 50th anniversary celebrations, visit www.sussex.ac.uk/fiftyyears