After a gruelling nationwide tour, a dozen hustings and three televised debates, Liz Truss appears poised to take over as the UK's next prime minister heading into the close of voting by Conservative party members on Friday.

The result of the summer-long campaign pitting the foreign secretary against former chancellor Rishi Sunak will be announced on Monday, before Prime Minister Boris Johnson formally tenders his resignation to Queen Elizabeth II the next day.

Postal and online voting by the estimated 200,000 Tory members began in early August, a month after Johnson announced his resignation, and concludes at 5:00 pm (1600 GMT).

Truss enjoys overwhelming support over Sunak in polling of the members.

But the winner faces a vanishingly short political honeymoon once they return to 10 Downing Street from meeting the queen in the Scottish Highlands.

The UK is in the throes of its worst cost-of-living crisis in generations, with inflation soaring by double digits as energy prices rocket on the back of Russia's war in Ukraine.

Millions say that with bills set to rise by 80 percent from October -- and further from January -- they face a painful choice between eating and heating this winter, according to surveys.

Truss has vowed tax cuts but those would do nothing to benefit the poorest.

For weeks, the Tory front-runner has been ruling out direct handouts, and went further at the final hustings Wednesday by repeating former US president George Bush's promise of no more taxes -- which he soon broke.

But writing in Thursday's edition of The Sun newspaper, Truss vowed to "deliver immediate support to ensure people are not facing unaffordable fuel bills" this winter.

"I firmly believe, in these grave times, we need to be radical," she added, previewing her Thatcherite agenda of reform to cement Johnson's Brexit legacy.

- Challenge -

Tory MPs turned on their Brexit hero Johnson after months of scandal, and favoured Sunak over Truss as the more electable leader to take them until the next general election due by January 2025.

But the party's rank and file have rallied to Truss's right-wing platform, even if she is a former Liberal Democrat who opposed leaving the European Union in Britain's 2016 referendum.

"She's a better politician," John Curtice, professor of politics at the University of Strathclyde, told AFP after Truss stuck to a simple script over the long, hot summer of campaigning.

"Sunak has demonstrated some of the qualities you might hope to see in a good minister. But Miss Truss has demonstrated the qualities that you need in a politician," Curtice added.

However, whoever wins, recent polls of the wider electorate show the Conservatives face a growing challenge to retain their 12-year grip on power.

The Labour party has profited from attacking Johnson's "zombie government" as the Conservatives have taken their time electing a new leader, gripped by infighting despite the wider crisis.

The main opposition party now boasts a double-digit lead over the Tories in opinion polls, as the economic landscape turns the bleakest it has been since Margaret Thatcher won power in 1979.