Rishi Sunak claimed his Tory leadership opponent Liz Truss has questions to answer about whether she would maintain the windfall tax on oil and gas profits.
Mr Sunak also pushed back at suggestions he has already lost the contest to be the next prime minister, saying many Conservative members were yet to make up their minds.
The two contenders are facing continued scrutiny to address rising living costs, as the latest predictions suggest energy bills could top £5,000 by the spring.
Mr Sunak has said he would consider using Government borrowing as a last resort to help struggling households while Ms Truss’ stance on “handouts” appears to have softened.
In an interview with Times Radio, Mr Sunak defended the windfall tax he had implemented as chancellor, claiming it would “automatically raise more money” in tax to support struggling households as energy profits increase.
The former chancellor added: “I think that is the right thing to do and I think Liz Truss last night said she opposed doing that, and actually didn’t believe in that policy, so I think that is a question for her to answer.”
He also claimed his opponent’s plans to cut taxes would do “virtually nothing” for pensioners or the least well-off.
A Sunak campaign spokesman added that Ms Truss had “blown a further £5 billion black hole in her plans” by not backing the windfall tax.
The former chancellor also pushed back when told Ms Truss is the frontrunner in the polls, saying: “I’m fighting passionately for the things that I believe are best for this country and the reception I’m getting everywhere I go is positive, people are responding well and I think I’ve got a fantastic chance to make progress in this campaign.”
Mr Sunak added that “lots of people have not made up their mind”.
The former chancellor is prepared to find up to £10 billion of extra support for those facing rising bills in the autumn, he wrote in the Times newspaper.
Mr Sunak also refused to rule out “some limited and temporary one-off borrowing as a last resort to get us through this winter”.
At a hustings in Cheltenham on Thursday, his opponent said she would “absolutely” not support a windfall tax, claiming it is a “Labour idea”.
“It’s all about bashing business, and it sends the wrong message to international investors and to the public,” Ms Truss said.
She insisted that profit is not a “dirty word” and argued that it being treated as such is “a massive problem”.
Mr Truss has previously hinted she would consider further support for struggling households if made prime minister, but insisted she will not “write the Budget in advance”.
One of her campaign allies, the Work and Pensions Secretary Therese Coffey, told broadcasters on Friday that “absolutely every option”, including further handouts, will be considered when it comes to support with the cost of living.
“People are going to get help. I think it is about what change in help may be needed, but help is already being given and will be given in the future as well,” added the minister.
On Thursday, Boris Johnson appealed to electricity bosses to help ease the pressure as on hard-pressed families.
Representatives of major electricity companies arrived in Downing Street for crisis talks as analyst, Auxilione, said regulator Ofgem could be forced to raise the price cap for the average household to £5,038 from next April.
However the meeting failed to produce any immediate concrete help for struggling consumers, with Mr Johnson acknowledging any “significant fiscal decisions” would be a matter for his successor.