Conservative Party chairman Andrew Stephenson thanked both candidates for taking part in the often “gruelling schedule in good spirits”.

“I know our party is ready to unite around a new leader and tackle the challenges we face as a country ahead,” he said as the ballot closed.

Voting by the estimated 200,000 Conservative Party members began in early August, a month after Johnson announced his resignation following a slew of scandals and resignations from his government.

Truss, 47, has consistently enjoyed overwhelming support over Sunak in polling of party members. She has campaigned to slash taxes and prioritise economic growth above all else, just as Britain faces decades-high inflation and is tipped to enter recession later this year.

“I have a bold plan that will grow our economy and deliver higher wages, more security for families and world-class public services,” Truss said in a statement, as the curtain came down on the often bitter race with her 42-year-old rival Sunak.

“If I am elected prime minister, I will never let anyone talk us down and I will do everything in my power to make sure our great nation succeeds.”

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Sunak has assailed Truss’s plans as “reckless”, warning they risk heightening inflation and eroding the country’s standing in the eyes of international lenders and markets.

He has argued that his experience guiding the country’s finances through the pandemic leave him best placed to lead the UK during its current economic woes.

“We face huge challenges ahead, but also huge opportunities”, Sunak said on Friday.

“I know what it takes to get through challenging times. I did it as chancellor and I will do it again as prime minister.”

Tory MPs turned on their Brexit hero Johnson after months of mishandling controversies, 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.

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Boris Johnson’s rise to power and what led to his downfall as UK prime minister

Boris Johnson’s rise to power and what led to his downfall as UK prime minister

“She is a better politician”, John Curtice, professor of politics at the University of Strathclyde, said 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.

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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.

Millions say that with energy bills set to spike by 80 per cent from October – and further again from January – they face a painful choice between eating and heating this winter.

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

She had previously decried direct handouts, but this week vowed to “deliver immediate support to ensure people are not facing unaffordable fuel bills” this winter.