‘You’re a nasty piece of work’: Boris trampled on in brutal interview

Boris Johnson struggled under pressure this morning during an unusually bruising BBC interview which shone a light on the difficulties he might face if he became Tory leader.

The London mayor looked uncomfortable and increasingly angry as he was asked about controversial moments in his past, including the accusation he plagiarised while at the Times, that he lied to his then-party leader Michael Howard over an affair and that he conspired to have someone assaulted.

"What does that say about you?" the stand-in host of the Andrew Marr Show, Eddie Mair, asked.

"Making up quotes, lying to your party leader, being part of someone being assaulted – you're a nasty piece of work."

Watch: Boris Johnson struggles in harsh TV interview

Johnson, who repeatedly asked "why don't we talk about something else", tried to avoid questions about his past and focus on issues around London housing stock and bids for Olympic venues.

"All three things I would dispute," he said.

"All three interpretations you're putting on those things isn't entirely fair.

"I did humour him in a long phone conversation from which absolutely nothing eventuated. If any of us had our phone conversations bugged… people say all sorts of fantastical things when talking to a friend."

The mayor refused to confirm that he wanted to be Tory leader, despite a seeming tacit admission on the point in tomorrow's BBC 2 profile, 'Boris Johnson: The Irresistible Rise'.

Branding leadership speculation "hysterical", he added: "All I want is for David Cameron to win this election. I want to do everything I can to help.

"People will rightly conclude I don't want to talk about this subject.

"It's a measure of the triviality of politics that I thought I was coming on to talk about the Budget and housing in London.

"[The public] don't care about phone conversations with my friends, they don't care about a ludicrous made-up quote, what they care about is what is happening in the UK economy."

Asked why he even appeared in the programme, Boris said it was safer to be involved than to let it all go ahead without his input.

"We faced a choice to help or rather prissily stand on the side," he said.

"It seemed sensible to say something rather than leave the all-clear to put the boot in."

That seemed an unusual piece of reasoning, given the London Mayor has turned down most requests for interviews on documentaries, having only accepted an episode of 'Who Do You Think You Are?'.

Asked whether he would watch the programme, Johnson replied: "I'm certainly not going watch it, not after what you told me."