At her first parliamentary grilling as British prime minister, Liz Truss on Wednesday confirmed plans to stem huge rises in the cost of energy that threaten to plunge her new government into a winter of discontent.

Jousting with opposition Labour chief Keir Starmer for the first time since she succeeded Boris Johnson, Truss also revelled in her status as the UK government's third female prime minister, noting Labour has still to elect a woman leader.

Truss ruled out a windfall tax on energy firms' gargantuan profits, but said details of her plan would be released on Thursday to ensure consumers and businesses can still afford heating in the coming months.

Whereas Johnson used the weekly session of "Prime Minister's Questions" to theatrically attack Starmer, Truss was more business-like as she pledged a right-wing programme of tax cuts to revitalise the UK economy.

Starmer cast Truss as the inheritor of 12 years of Tory government leading up to the present crisis in inflation, which is tied to Russia's war in Ukraine, and said there was "nothing new" about her policies.

"There's nothing new about a Labour leader who is calling for more tax rises," Truss retorted, earning roars of approval from Conservative MPs -- most of whom had initially backed her leadership rival, Rishi Sunak.

Johnson's predecessor Theresa May archly asked Truss why only the Conservatives had managed to elect women leaders -- May herself, and Margaret Thatcher. One Tory backbencher shouted "3-0!"

Starmer's deputy Angela Rayner looked on with a pained expression as Truss said it was "extraordinary" that Labour could not find a woman leader, or one who did not live in left-leaning North London.

Earlier Wednesday, Truss convened her new-look cabinet, which includes the most diverse top team in British history: Kwasi Kwarteng as finance minister, James Cleverly as foreign secretary and Suella Braverman as interior minister.

Under the costly plans developed by Truss and Kwarteng, gas and electricity bills for both households and businesses are expected to be capped near current levels for the coming winter at least.

The government would lend or guarantee private-sector loans to energy providers to make up the difference they pay from soaring global wholesale prices, which have driven UK inflation above 10 percent.

The spike in inflation to 40-year highs has stoked a wave of strikes, including by railway workers and criminal lawyers, with more sectors threatening to walk out in an early challenge to Truss's administration.

On the eve of Truss's energy plan announcement, the British pound slumped to its lowest dollar level since 1985, tanking to $1.1406 at about 1400 GMT.

Along with the urgent issue of energy prices, Truss's government must also navigate the combustible problem of post-Brexit trading arrangements in Northern Ireland.

In her first contacts with foreign leaders, the new Conservative leader spoke late Tuesday by phone to Ukraine's Volodymyr Zelensky and then US President Joe Biden.

According to Downing Street, she agreed with Biden "on the importance of protecting" peace in Northern Ireland.

In parliament, Truss said she was "determined" to break through the impasse, and favoured a "negotiated settlement" with the EU.

To Zelensky, Truss vowed to maintain the full-throated support for Ukraine against Russia given by Johnson before he was forced out following a series of scandals.

Truss, 47, won an internal ballot of Tory members on Monday, securing 57 percent of the vote, after a gruelling contest against former finance minister Sunak that began in July.

She now faces a tough challenge reuniting the ruling Tories following the leadership battle, but observers noted that she had expelled almost every Sunak supporter from the cabinet.

Ex-soldier Johnny Mercer said he was "disappointed" to be sacked as veterans affairs minister.

His wife Felicity Cornelius-Mercer went further, calling Truss an "imbecile" as she tweeted a picture mocking the new prime minister as a dim-witted character from "The Muppets".

The Times quoted one of her incoming ministers as saying: "I doubt she'll last two years."

A general election is due by January 2025 at the latest. Truss on Wednesday again ruled out an early election, mindful perhaps that she needs time to win over a sceptical electorate after Johnson's defenestration.

A new poll by Ipsos found just a third of people expect Truss to do a good job as prime minister, while another third say she will do a bad job.