British Prime Minister Liz Truss said she would set out plans to tackle soaring energy bills on Thursday but would not impose a windfall tax on energy producers, with borrowing instead set to increase to fund the costly intervention.

Truss, appointed prime minister on Tuesday, has vowed immediate action to address one of the most daunting sets of challenges for an incoming leader in post-war history including soaring energy bills, a looming recession and industrial strife.

She chaired a meeting of her new cabinet on Wednesday before making her parliamentary debut as Conservative Party leader, going head-to-head with opposition Labour Party leader Keir Starmer in the high-profile Prime Minister's Questions.

"I am against a windfall tax. I believe it is the wrong thing to be putting companies off investing in the United Kingdom," Truss told lawmakers, adding she would announce more details on Thursday.

A source familiar with the situation told Reuters that Truss was considering freezing energy bills in a plan that could cost towards 100 billion pounds ($115.33 billion), surpassing the COVID-19 furlough scheme.

New finance minister Kwasi Kwarteng told business leaders that borrowing would be higher in the short term to provide support for households and businesses.

Investors have expressed alarm at the scale of extra borrowing that the government will probably need to undertake to fund its support scheme and the tax cuts promised by Truss during her leadership campaign.

The pound sank to two-and-a-half-year lows against the dollar this month while long-dated British government debt fell on Tuesday by the most since the onset of the COVID-19 pandemic, adding to a recent slump. [GBP/] [GB/]

Bank of England officials told lawmakers that Truss's plans could help to slow Britain's surging inflation, but it was too soon to say what the implications for interest rates would be.

Truss's first parliamentary appearance as PM saw her lawmakers cheer her entrance, receiving loud support when she went toe-to-toe with Labour' Starmer.

Former leader Theresa May drew applause when she pointed out that Truss was the third female Conservative prime minister, while all Labour leaders have been men.

Truss was chosen by Conservative members running on a low tax platform and her clash with Starmer, who asked why she would not consider a windfall tax to fund her energy plan, set out the ideological divide between the two leaders starkly.

"There is nothing new about a Labour leader who is calling for more tax rises. It's the same old same old tax and spend," she said, to cheers.