London mayoral candidates Zac Goldsmith and Sadiq Khan clashed over race in a fierce head-to-head debate as tensions between the two camps continue to grow.
Mr Khan said he was "disappointed" by the tone of his Tory opponent, amid accusations Mr Goldsmith is running a racist campaign.
But in a passionate response Mr Goldsmith said the Labour hopeful was using claims of Islamophobia to "close" down questions over his "judgment".
The tense exchange came after comments by former minister Yvette Cooper, who told The Times newspaper's Red Box website that Mr Goldsmith's "subtle dog-whistle is becoming a full-blown racist scream".
In his opening statement Mr Khan said: "I've been disappointed by the tone of the campaign run by my opponent. It's been negative. It's been divisive.
"I'll continue to be an advocate for the best of London. A mayor who can unite our city not divide it."
Mr Goldsmith hit back at the allegations, arguing it was right that Mr Khan was being scrutinised.
He said: "In recent days Sadiq Khan and his supporters have accused my campaign of being Islamophobic.
"Sadiq, I have never referred to you by your religion. That has simply never happened. To suggest otherwise is wrong and it is offensive.
"It is irrelevant to anyone's ability to do this job. But there are serious questions about you and your judgment."
He added questions should be raised over Mr Khan sharing platforms with people with extremist views.
Mr Goldsmith continued: "You shout Islamophobia to close those questions down. But this is nothing to do with Islam.
"Nor is anyone suggesting Sadiq that you have extreme views. This is very simply about your judgment."
The criticism against Mr Goldsmith, the Tory MP for Richmond Park, centres on claims he is targeting specific ethnic groups in the capital for mail-shots.
The pair, who were speaking at an event organised by business newspaper City.AM at the Institute of Directors, London, exchanged blows on the EU referendum, transport and housing policy.
They were forced by an audience member's question to acknowledge each other's strengths.
Mr Khan said he knew his opponent as a "personable" character and found him "good company".
But he added: "I'm sorry that he is allowing those running his campaign to lock away the real Zac Goldsmith and put forward this person that I don't recognise."
The Tory MP did not respond to the comments but said he thought it "admirable" that Mr Khan was such a "gritty campaigner".
The candidates also clashed on their involvement with Babar Ahmad, who was extradited to the US for his links to terror groups.
Mr Goldsmith criticised Mr Khan for campaigning "very actively" on his behalf.
But the Labour candidate said he was "amazed at the selective amnesia" of Mr Goldsmith, who he suggested had also campaigned to stop Ahmad from being extradited.
Mr Goldsmith dismissed the claims as "complete and utter nonsense".
He said he had campaigned against "unfair" extradition rules but had not heard of Ahmad until "quite recently".