Author Philip Pullman may have attracted the biggest crowds at the Oxford Literary Festival, but it was the appearance of political heavyweights Alastair Campbell and Tony Benn that captured the imagination.

Mr Benn, the veteran champion of Old Labour, made an unlikely double act with Mr Campbell, the man dubbed as the second most powerful man in Britain under former Prime Minister Tony Blair.

Although he has retired from the political fray, Mr Campbell showed no sign of mellowing as he discussed his controversial diaries.

And he revealed he is ready to reignite his battle with the BBC, sparked by a radio interview at the centre of the Hutton Inquiry into the death of Oxfordshire-based weapons expert Dr David Kelly.

Mr Campbell said the suicide of Dr Kelly, who lived in Southmoor, near Abingdon, was the darkest moment during his years at Mr Blair's side.

He said: "It was the worst thing that happened in the entire period I was in Government. It was impossible not to feel that very deeply."

But he told an audience at Christ Church he remained convinced the tragedy would not have happened but for what he claimed was inaccurate BBC journalism on Radio 4's Today programme.

And he returns to the attack on the BBC when his diaries appear in paperback next month.

The introduction will give his version of sharp exchanges with John Humphrys on the Today programme when the diaries were first published.

He said: "I thought long and hard about whether I wanted to do the interview but decided it would have been cowardly not to.

"I did the 8.10am spot on the day the book came out and after 20 minutes I began looking at my watch."

He believed the length of the interview reflected Today's determination "to get something on him."

He accused the media of having become obsessed about his role as a spin doctor.

He said: "The reason they loathe me as much as they do, is because I don't care what they think or say about me.

"I have reached the point where I don't read newspapers and I don't feel any less well informed."

Mr Campbell defended his decision not to include new revelations in his diaries about rows between Gordon Brown and Tony Blair.

He said: "I go back a long way with Gordon, further than I do with Tony."

Mr Benn, the father of environment secretary Hilary Benn, joked that he was now able to use a free Oxford bus pass.

Now aged 83, he spoke about his diary, the writing of which began when he was aged just 15.