Differences between David Cameron and a major Conservative donor have burst into the open with the serialisation of a book containing allegations about the Prime Minister's time as a student.
The claims relating to his alleged youthful excesses are in a book entitled Call Me Dave by billionaire peer Lord Ashcroft and journalist Isabel Oakeshott, serialised in the Daily Mail.
The book also alleges that Mr Cameron was aware Lord Ashcroft had not given up his controversial "non dom" tax status when he joined the House of Lords earlier than was previously admitted.
Downing Street has declined to comment on its contents, which are likely to cast a shadow over the Conservatives' upcoming annual conference in Manchester.
"I am not intending to dignify this book by offering any comment," the Prime Minister's official spokeswoman said. "He (Lord Ashcroft) has set out his reasons for writing it. The Prime Minister is focused on getting on with the job of running the country."
Sources close to the Prime Minister said they "did not recognise" the accusations, which include claims Mr Cameron was present at events where drugs were taken and was part of a decadent Oxford University dining society.
It is claimed that as a member of the Piers Gaveston society - named after the lover of Edward II - Mr Cameron took part in a bizarre initiation ceremony which involved him inserting "a private part of his anatomy" in the mouth of a dead pig.
Lord Ashcroft said that he was told about the incident by an Oxford contemporary of Mr Cameron who is now an MP and who claimed to have seen a photograph of the event.
The authors said that they attempted to contact the owner of the alleged photograph but received no response.
In the book, due to be published next month, Lord Ashcroft acknowledges he has a personal "beef" with the Prime Minister after his failure to offer him a significant job in his administration following the formation of the coalition government in 2010.
He claimed the PM initially blamed Liberal Democrat coalition partners for blocking his appointment, before offering him a junior role at the Foreign Office which he described as "declinable", adding: "It would have been better had Cameron offered me nothing at all."
Made a life peer by William Hague in 2000 after saving the party financially as treasurer in the wake of its disastrous 1997 election defeat, Lord Ashcroft has given around £8 million to the Tories and was deputy chairman during Mr Cameron's period as leader in opposition.
In his book, Lord Ashcroft claims that as early as 2009 he spoke with Mr Cameron about how to delay revealing his "non-dom" tax status - which allowed him to avoid tax on overseas earnings - until after the following year's general election.
This contradicts a Conservative assertion at the time when the controversial status became known in 2010 that Mr Cameron had been told only a month before.
Lord Ashcroft - who had given a commitment to become resident in the UK for tax purposes when he was made a peer - subsequently gave up his non-dom status in order to retain his place on the Conservative benches in the Lords.
The book also describes how the Tories' Australian spin doctor Lynton Crosby described Mr Cameron as a "posh c***" while he was working in the Conservative Campaign HQ during the 2005 general election.
Asked about Lord Ashcroft's allegations at a press conference during his visit to China, Chancellor George Osborne said only: "I haven't seen that book."
Liberal Democrat leader Tim Farron told Sky News the allegations were "extraordinary" but "a bit of a sideshow".
He said: "The reality is we respect people's right to a private life and a past. The critical thing in all of this is that those of us who are in politics mustn't be hypocrites."