Tory leadership hopeful Rishi Sunak has pledged to scrap the 5% VAT rate on household energy bills if prices continue to rise later this year.
The former chancellor, who has not promised tax cuts so far in his campaign, said the plan would help families with rising living costs.
Rival Liz Truss's campaign team described the move as desperate - accusing him of a "screeching U-turn".
Meanwhile rival Ms Truss has pledged to cut key crime rates if she wins.
She also said police forces would be encouraged to send an officer to every burglary.
The latest pledges come after a live TV debate between the two contenders on Tuesday night was halted and taken off air halfway through when presenter Kate McCann fainted.
TalkTV, which was co-hosting with the Sun newspaper, said its journalist McCann was "fine" but it had been given medical advice not to continue.
Viewers watching the debate saw Ms Truss giving her answer to a question and then react with surprise then concern as a crashing noise was heard off camera.
The VAT announcement marks a tactical shift from Mr Sunak, who is trailing in opinion polls of Conservative party members, who will be the ones selecting the winner when they vote over the next month.
Under his "winter plan", the 5% VAT rate on household energy would be scrapped for one year from October, if the price cap on bills rises above £3,000 for the typical household.
He added that the "temporary and targeted" tax cut would save average households £160 a year, and ensure people get "the support they need" while also "bearing down on price pressures".
It contrasts with his approach as chancellor, when he argued against a Labour plan to scrap energy VAT earlier this year and said the policy would "disproportionately benefit wealthier households".
Mr Sunak, who has accused his rival Ms Truss of making unfunded tax cuts that amount to £55bn, said his plan would cost £4.3bn but argued that as it was temporary it could be delivered within existing borrowing rules.
He has also promised to double the number of hours benefit claimants have to work before they can stop attending appointments with work coaches from 9 to 18 hours per week.
Work and Pensions Secretary Therese Coffey, a Truss supporter, argued Mr Sunak had blocked a move to raise the limit to 12 hours earlier this year.
In announcements of her own, Foreign Secretary Mr Truss said she would set police forces a target of cutting homicide, serious violence and neighbourhood crime by 20% before the end of the current Parliament.
Her campaign said she would publish league tables per force, with underperforming areas invited to a special meeting chaired by the home secretary.
A campaign source accused some chief constables of "not cracking down as hard as they should be".
But the Sunak campaign dismissed the proposals, calling them a "lightweight plan based on publishing data the government already does".
Source: BBC
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