Ken Livingstone and Boris Johnson clashed furiously over their tax arrangements in the first live debate ahead of the mayoral elections.
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.
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."
More top news
A 14-year-old boy has been charged after a man was shot dead and three people were injured in a shooting at a US primary school.
Sunshine with blustery showers and longer downpours
The founder of a free school and two ex-staff members have been jailed for defrauding the Department for Education of thousands of pounds.