Boris Johnson's rivals rounded on him over his ambition to give people earning more than £50,000 a tax cut, as the Tory leadership contest turned increasingly bitter.
Just hours after clearly winning the second round of voting among Tory MPs, Mr Johnson faced his opponents in a TV studio for the first time, having ducked the previous televised debate.
He came under fire for his tax plans, and was also taken to task over his comments comparing veiled Muslim women to "letterboxes" and "bank robbers".
Just hours after Dominic Raab was eliminated from the race in the second round of voting, Mr Johnson was joined in the BBC debate by his remaining rivals – Jeremy Hunt, Michael Gove, Sajid Javid and Rory Stewart.
Mr Johnson said he would lift the National Insurance threshold for the low-paid, but there should be a "debate" about the 40p higher income tax rate, which currently kicks in at £50,000.
"It does seem to be very odd that in the Conservative Party people should seriously question whether it is right to try to lift nurses and heads of maths departments and police inspectors out of the top rate of tax," he said.
But Foreign Secretary Mr Hunt said people accused the Tories of being "the party of the rich" and "we must never fall into the trap of doing tax cuts for the rich and confirming that prejudice".
Environment Secretary Mr Gove said "cutting taxes for folk who earn what MPs earn and what millionaires earn, I think that is wrong".
Mr Stewart, whose campaign has gained momentum as the contest has continued, hit out at his rivals for making promises on Brexit and taxes that they could not keep.
Calling for "honest and realistic" politics he said: "The thing that slightly depresses me in this debate is everybody is promising things – they are promising they are going to get a new deal out of Brussels, that they are not going to get, they are promising they are going to get a no-deal through Parliament, which they can't deliver.
"And they are now promising – cumulatively, all of them together – have promised nearly £84 billion worth of tax cuts."
Mr Stewart said money should be spent on public services rather than cutting taxes.
During the debate the candidates clashed over Brexit:
– Mr Stewart insisted that Theresa May's Withdrawal Agreement was the only route out of the European Union, while "everybody else is staring at the wall shouting 'Believe in Britain'."
– Mr Gove said the Withdrawal Agreement had already been rejected three times and "you cannot simply re-present the same cold porridge for a fourth time and ask people to say that's what they want".
– Mr Johnson said the October 31 deadline for leaving the EU must be met "otherwise, I'm afraid, we face a catastrophic loss of confidence in politics".
– Mr Javid said it had been a "mistake" to have a flexible deadline, and the October 31 date would concentrate minds on both sides of the Brexit negotiations.
– Mr Hunt said he would delay beyond October 31 if a deal was in reach, as "if we were nearly there, then I would take a bit longer", a point echoed by Mr Gove, who said he would allow "extra time" to be played to secure an agreement.
Mr Johnson had earlier built on his lead in the ballot of Tory MPs, securing 126 votes – 12 more than the first round – putting him 80 ahead of Mr Hunt who had 46 votes, up three.
Mr Gove put on four votes to reach 41, while Mr Stewart surged into fourth place on 37, gaining 18 votes since last week.
Mr Javid scraped into the next stage of the contest, just meeting the threshold of 33 votes – a gain of 10 – while Mr Raab was eliminated with 30 votes.
Mr Johnson said he was "very, very pleased with the momentum" of his campaign but he was "still very much the underdog in this race".
There were allegations of dirty tricks, with claims that Mr Stewart's camp were already contacting Mr Javid's supporters by text message to get them to switch sides.
And Mr Javid's team also rejected suggestions that he had been lent votes by Mr Johnson's backers to ensure he stayed in the contest.
Campaign frontrunner Mr Johnson appears certain to be one of the final two names on the ballot paper which goes to the 160,000 Tory members who will choose the next party leader and prime minister, and the contest now appears focused on who will join him.
Until the BBC debate, Mr Johnson had steered clear of public appearances with his opponents.
He was challenged by the debate's host Emily Maitlis about a Daily Telegraph column in which he made the "letter boxes" jibe about Muslim women.
Mr Johnson said: "In so far as my words have given offence over the last 20 or 30 years, when I have been a journalist and people have taken those words out of my articles and escalated them, of course I am sorry for the offence they have caused."
During the same section of the debate Mr Javid called on all the candidates to commit to an external investigation into allegations of Islamophobia in the Tory party.