Boris Johnson's past troubles finally returned to haunt him yesterday when he gave what senior Conservatives called a "car crash" television interview which they said had dented his hopes of becoming Conservative Party leader.

The colourful Mayor of London is often treated with kid gloves by interviewers but Eddie Mair, who hosted the BBC's Andrew Marr Show, was wearing boxing gloves. He subjected Johnson to the awkward questions and scrutiny he could expect if he were running to be Prime Minister, rather than running the capital.

"You're a nasty piece of work, aren't you?" asked Mair. Johnson looked surprised and distinctly uncomfortable as the presenter asked him about his being fired by the Times newspaper for making up a quote; being sacked from the Tory frontbench for telling "a bare-faced lie" to the party leader Michael Howard about his affair with journalist Petronella Wyatt, and the claim that he agreed to provide a reporter's address to his friend Darius Guppy, a convicted fraudster, so the journalist could be beaten up.

An exasperated Johnson said he would "dispute" all three allegations. Only up to a point, it seemed. He admitted he had "mildly sandpapered something someone said" for the Times, saying it was "very embarrassing" and he was "very sorry". He insisted he never spoke directly to Howard about the affair, although at the time in 2004 he publicly denied it as "an inverted pyramid of piffle". He told Mair: "I could explain that I think all three interpretations you're putting on those things aren't wholly fair ... the case of my old friend Darius [Guppy] yes, it was certainly true that he was in a bit of state and I did humour him in a long phone conversation, from which absolutely nothing eventuated. But I think if any of us had our phone conversations bugged, they might, you know, people say all sorts of fantastical things whilst they're talking to their friends."


The softly-spoken, dry but deadly BBC presenter, told Johnson: "I want to talk about you." Revealingly, the mayor replied: "Well that's exactly what I'm trying to avoid."

The mayor complained that he had in effect been blackmailed by documentary maker Michael Cockerell into co-operating with a programme about him to be screened by the BBC in Britain today.

Asked about his ambitions, Johnson told Cockerell: "I think it's a very tough job being Prime Minister. Obviously if the ball came loose from the back of the scrum - which it won't - it would be a great, great thing to have a crack at it. But it's not going to happen."

Some of those interviewed by Cockerell were less than flattering about his subject. "Boris isn't pretending to be chaotic; he really is utterly chaotic," said Sir Max Hastings, his former editor at the Daily Telegraph. Conrad Black, who appointed Johnson editor of the Spectator magazine, describes him as "a sly fox disguised as a teddy bear".