Rishi Sunak and Liz Truss traded heavy blows in their first head-to-head TV clash as the Tory race descended into open warfare.
The former Chancellor hectored his ex-Cabinet colleague over her "unfunded" plans for £40billion in tax cuts that he claimed would tip "millions into economic misery".
But Ms Truss accused him of "Project Fear" as the pair trashed each other's economic plans in front of a live audience in Stoke-on-Trent.
In a bad-tempered clash, Mr Sunak repeatedly interrupted his Tory rival - prompting her camp to accuse him of being "not fit for office" due to his "aggressive mansplaining".
The BBC debate descended almost immediately into a slanging match as Mr Sunak hit out at her "short term sugar rush" economic policies - but Ms Truss rejected his "negative, declinist language".
The Foreign Secretary accused Mr Sunak of "Project Fear" after he claimed cutting taxes is not a moral or Conservative thing to do.
"This is scaremongering, this is project fear, scaremongering, it is."
In a fiery attack on Ms Truss' Remain-supporting past, Mr Sunak said: "I remember the referendum campaign and there was only one of us on the side of Project Fear and Remain and it was you, not me."
The race for No10 has become increasingly bitter, with Team Truss and the Sunak campaign trading barbs over their records and policy plans.
Senior Conservatives have pleaded with the rivals to stop bickering as they fear it is handing ammunition to Labour.
But blue-on-blue attacks show no sign of abating, as Mr Sunak scrambles to make up ground with Tory members who will determine the next PM.
Mr Sunak began the debate by hinting that he would consider energy bills help in the autumn when the energy price cap is due to rise again.
He said: "When we get in we will have to see what happens to energy bills, as the situation changes on the ground, I am always going to support people through it."
Ms Truss said she would "act immediately" and vowed to scrap the National Insurance hike imposed by the Government and put a halt on the green energy levy.
But Mr Sunak said it was not responsible or Conservative to "put it on the credit card" - and said she was pushing for £40billion of unfunded tax cuts.
Ms Truss says his plans are "contractionary" and would lead to a recession.
She said: "We know what happens when there's a recession. I grew up in Paisley and Leeds in the 1980s and 1990s.
"I know what it's like when people have to struggle when you have high unemployment and people don't have work to go to.
"We cannot allow that to happen."
But Mr Sunak said her plans would hammer Brits, pointing to comments from economist Patrick Minford, who has advised her campaign, that her plans would push up interest rates as high as 7%.
"It's going to tip millions of people into misery and it's going to mean we have absolutely no chance of winning the next election either," he said.
Tax has been a major battleground as the duo try to woo Tory members who will decide the next leader.
But the campaign has become increasingly personal, with Ms Truss forced to distance herself from her ally Nadine Dorries' attacks on Mr Sunak's expensive taste in clothes.
She said she would not give Mr Sunak fashion advice, describing him as a "very well-dressed man".
She said: "I don't think this is really the key issue in the campaign, frankly, you know, we have had a really serious discussion about the importance of growing the economy, and what will help achieve that.
"That's what people in Stoke-on-Trent want to hear about. They don't want to hear about Rishi and my fashion choices."
Mr Sunak was forced to defend his immense wealth again, but argued that his was a success story, saying: "I wasn't born this way."
"My parents were part of an immigrant family that came here," he said.
"They didn't start with very much, but they worked day and night, saved and sacrificed to provide a better future for their three children."
He ruled out letting Boris Johnson serve in his cabinet, saying it was time to "look forward".
But asked to rate the PM out of 10, he awarded him full marks for delivering Brexit.
Ms Truss said "I just don't think it's going to happen" but didn't explicitly rule out letting Mr Johnson back into Government.
Ms Truss invited Mr Sunak to be a part of her team at the end of the fractious contest but her team was less welcoming.
A spokesperson for Liz Truss said: "Rishi Sunak has tonight proven he is not fit for office.
"His aggressive mansplaining and shouty private school behaviour is desperate, unbecoming and is a gift to Labour."
Mr Sunak's team declined to comment on the accusation.
Labour's National Campaign Co-ordinator Shabana Mahmood said: “Neither Liz Truss nor Rishi Sunak offers working people anything except more of the same - low growth, high taxes, frozen wages, and longer waiting times.
“These two continuity candidates gave their now familiar chorus of unfunded spending promises, bitter attacks, and a trashing of the Tories’ 12 years in government.
"Neither offered anything resembling a plan to tackle the cost of living crisis they created or for a better future for the country.”
