September 22, 2015updated 28 Sep 2015 1:30pm

Co-author of Cameron book: We couldn’t ‘get to the bottom of’ pig story… so we reported source’s account

Former Sunday Times political editor Isabel Oakeshott has defended the biography of the Prime Minister she co-authored with Lord Ashcroft.

The book, Call Me Dave, which is being serialised in the Daily Mail, reports the allegation that David Cameron inserted "a private part of his anatomy" into the mouth of a dead pig when he was a student.

Appearing on Channel 4 News last night, Oakeshott claimed that the book “merely reported the account that the source gave us”.

Yesterday, a former News of the World political editor said the allegation – made by one “respected Tory MP”, according to Oakeshott – would not have made it into the tabloid because it would not have passed “basic tests”.

And Oakeshott refused to say on Channel 4 News last night whether her former newspaper, The Sunday Times, would have run the story.

"That's an entirely hypothetical question," she said. "I don't think that that's particularly worth responding to.

"We're very careful about the way we worded the story, and as I say it's up to people to decide whether they think it's true or not. We don't say whether we believe it to be true."

Oakeshott also told the programme: "Look, this was just a few paragraphs in the middle of a book which is some 200,000 words long. So let's look at the book as a whole when it comes out, and make judgment then.”

Told that she must have realised this would be a section of the book that would capture the public’s imagination, Oakeshott added: “First of all, let's be clear: this is not Lord Ashcroft and myself making these allegations… This story first came to us via a respected Tory MP who was a contemporary of David Cameron's at Oxford University.

“Now, when we first heard the story we assumed it was a joke. That source continued to repeat those allegations on a number of subsequent occasions. Now we couldn't get to the bottom of that source's allegation, so we merely reported the account that the source gave us.

“And it's up to other people to decide whether they give it any credibility or not.”