Talking to the BBC a day ahead of the Conservative leadership announcement, the foreign minister expected to succeed Mr Boris Johnson said: "If I'm elected prime minister, I will act immediately on bills and on energy supply."
She declined to give details before her appointment is confirmed, saying simply: "Within one week I will make sure there is an announcement on how we are going to deal with the issue."
The Tory leadership race has stretched over eight weeks as Britain faces decades-high levels of inflation and is tipped to enter recession later this year. British households are facing an eye-watering 80-per-cent average hike in electricity and gas bills, in a dramatic worsening of the cost-of-living crisis before winter.
Ms Truss, 47, has topped polls among the estimated 200,000 Conservative Party members who pick the next leader, outshining her rival Rishi Sunak, the 42-year-old former finance minister.
Ms Truss previously decried direct handouts, but last week vowed to "deliver immediate support to ensure people are not facing unaffordable fuel bills" this winter.
Ms Truss's campaign has promised tax cuts but critics note those would do nothing to benefit the poorest. On Sunday she stressed she believes tax cuts that benefit the wealthy are fair and promote growth.
"To look at everything through the lens of redistribution (of wealth), I believe is wrong," she said.
Mr Sunak has promised further government support to help people pay their energy bills and said curbing inflation would be his priority, attacking Ms Truss's tax-slashing plans as reckless.
"Helping people with the cost of living and energy bills comes above everything else that I might like to do," he told the BBC on Sunday.
Mr Sunak appeared to accept his likely defeat and offer backing to Ms Truss, saying that if he loses: "I look forward to supporting the Conservative government in whatever capacity" and confirming he would stay on as an MP.
The announcement of the next party leader, who will become prime minister, will be made on Monday at 1130GMT (7.30pm Singapore time). Queen Elizabeth II will then formally appoint Mr Johnson's successor on Tuesday. AFP