Boris Johnson, the politician with the amiable air of a man who never cracks under pressure, completely lost it yesterday. After months of stressful campaigning in the run-up to May's London mayoral election, he finally let his rival, Ken Livingstone get under his skin.
In a crowded lift, in front of three witnesses, the Mayor met the former Mayor in a nose-to-nose confrontation, and called him a "f***ing liar" three times over.
The explosion occurred after the four main candidates in the mayoral contest had taken part in a hustings hosted by LBC radio station. It was witnessed by the Liberal Democrat candidate, Brian Paddick, Green candidate Jenny Jones, and an LBC executive.
The most damaging setback for Ken Livingstone in the campaign so far has been the revelation that for years his substantial media earnings were paid into private companies, attracting corporation tax at 20 per cent rather than the higher rates of income tax.
Having been challenged again yesterday about his tax arrangements, Livingstone went on the attack and accused Johnson of channelling his money through a firm called Finland Station.
That clearly annoyed Johnson, who asserted: "I have never used a company to minimise my tax. There was a TV production company which I was briefly a director of but I have always paid full income tax."