David Cameron has said he will not sue Lord Ashcroft over claims published from the controversial biography last week, because he is "too busy running the country".
He reacted to Conservative donor Ashcroft's latest tell-all text, saying people would "see right through it".
Cameron was responding for the first time to salacious tales circulated among newspapers and on social media regarding a bizarre student ritual he was said to have taken part in involving a dead pig.
Having first not dignified the claims with comment, the Prime Minister rowed back from his original position Monday, snubbing the spurious story.
"Frankly this book was written for a very clear reason and I think everyone can see right through it," he told Sky News.
Quizzed on whether he would take legal action against Lord Ashcroft, Cameron said: "No, I'm too busy running the country taking decisions, getting on with work.
"If you do a job like this, you do get people who have agendas and write books and write articles and write all sorts of things. The most important thing is not to let it bother you and get on with the job."
The PM was also probed on further claims made last week saying he knew earlier than previously admitted that Lord Ashcroft received special 'non-domicile' tax-exemption status.
Cameron said: "I dealt with all of that before the election and indeed we made a law to make sure you couldn't be a non-dom and sit in Parliament."
The news comes after Labour's leader, Jeremy Corbyn, himself spoke out over the furore, saying too much attention paid to last week's scandalous allegations risked overshadowing "real issues".
He blasted media outlets for obsessing over the claims, criticising journalists for having become obsessed with "personality politics".