Boris Johnson and Ken Livingstone clashed furiously over their tax arrangements today in the first live debate ahead of next month's London mayoral elections.
In a fractious session hosted by radio station LBC 97.3, Mr Johnson denied suggestions he had used a company to channel his media earnings to avoid paying income tax - a claim that he has levelled at his Labour opponent.
Mr Livingstone accused the mayor of having "the same arrangements" for dealing with his media earnings as he had, insisting he had used a company called Finland Station.
But Mr Johnson called the claim "lies", adding: "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 certainly never ... I have always paid full income tax."
Later, the row between the pair continued off-air when a furious Mr Johnson swore at his Labour opponent.
Travelling in a lift to the top of the LBCD building to be photographed, the Mayor shouted at Mr Livingstone "it's all f****** lies, it's all f****** lies".
In recent weeks Mr Livingstone has come under attack over claims he used a private company to ensure he only paid corporation tax at 20pc on his media earnings.
Mr Johnson was said to be outraged when the Labour candidate attempted to claim during today's public debate that he adopted the same practice.
It is understood the Mayor talked to his opponent privately after a business hustings three weeks ago to tell him what he had been saying about his tax arrangements was not true.
Today, Mr Johnson issued a statement rebutting the allegations over his tax affairs.
He said: "In relation to my business affairs and tax arrangements, specifically do I have any company or other arrangements constructed to enable me to pay less tax and do I, as has been claimed by the Labour mayoral candidate and the opposition leader
"My salary as mayor is taxed as an employee of the GLA. In the same way as when I was an MP my salary was taxed as an employee.
"Any other income that I have received from outside endeavours has been received on a self-employed basis, to me as an individual (no company or other structure has been involved).
"Of course the real point is not about my tax arrangements. It is about the hypocrisy of a man who for years has railed against those who use special arrangements to reduce their tax and who has then been caught - bang to rights - doing the very same thing himself."