Mayor Boris Johnson was caught in a fiery exchange with Ken Livingstone on Wednesday night, accusing his Labour opponent of "playing politics" over last year's London riots.
This war of words came as the leading mayoral candidates met at their largest public debate yet, held in the Emmanuel Centre for the London Evening Standard.
Livingstone took a swipe at Johnson for the time he took to return to London after the riots broke out.
"It was a catastrophic misjudgement. If you loved this city you'd want to be here when things go wrong" he shouted, to loud applause from the audience.
Johnson responded, to boos, by branding Livingstone's "attempts to play politics" with the riots as "very low".
"I was in a caravan stuck up a mountain with very poor mobile reception and I was a good 300 miles from the nearest airport. As soon as it was obvious what was going on, I got back as fast as I could," he added.
The candidates discussed their plans to improve London transport. Johnson launched an attack on Livingstone's plans to reduce fares as, he argued, infrastructure investment would suffer.
"It's complete codswallop to say there's a surplus in the TFL budget [to pay for fare cuts]. It's utter baloney. Ken needs to level with Londoners about where the money is coming from," he said.
Livingstone suggested his plans were based on TFL documents, adding that his planned 7% fare cut would be the "smallest" in his career.
Liberal Democrat candidate Brian Paddick quipped: "All these numbers get thrown around and who knows who can make sense of them!"
Paddick also came to the Mayor's defence on his transport policy. "While Boris plays the fool, he's not stupid. If he had the money to reduce fares before an election - surely he would have done it?" he said.
The candidates also discussed their tax arrangements. Green Candidate Jenny Jones admitted that she just "blurted out" her request on Newsnight that the candidates should publish their tax returns, saying she was "exasperated" with the nature of the debate.
Johnson touched on reports that he had confronted Livingstone in an explosive argument in a lift about tax arrangements. "I felt entitled to correct him in a pithy and frank way," he joked.
Livingstone declared that the tax furore had been stoked up by his opponents as a "complete distraction" from serious political issues. He claimed that the details he published of his tax arrangements "lanced the boil". The Labour candidate was a bit flustered as he faced heckles from the audience to "give it back!" and "resign!"
The mayoral debate was briefly disrupted by BNP Mayoral candidate Carlos Cortiglia, who complained about the "democratic problem" since he and two other mayoral candidates were not represented at the debate. He was brushed off and remained at the back of the theatre, waving a paper for attention in vain.
David Coburn, UKIP candidate for Bexley & Bromley, told HuffPost UK that the debate was "very tame".
"Everyone avoided answering the questions. They're determined to keep Ukip off the airwaves and out of everything. The Greens have only got 3% but we are on 11% and it looks like we are going to get 3 or 4 London Assembly candidates."
Independent Candidate Siobhan Benita accused the candidates of not talking about youth issues. She later told the Huffington Post UK that there were a "lot of issues that they didn't talk about enough."
"The debate was not particularly challenging. They only mentioned housing at the end and barely anything about youth issues," she added.
Benita also received support from Brian Paddick - who said he wished she could be on stage debating too as they are "almost" alike. She was cynical, when speaking to us, about whether he was sincere: "The candidates may say that [they want me included] but do they really mean it?"