London (AFP) - Rishi Sunak will on Tuesday be installed as Britain’s third prime minister this year, after the humiliated Liz Truss left office after just 49 days, with the new premier inheriting a daunting array of problems.

Departing Downing Street, Truss wished Sunak “every success” and said she remained “more convinced than ever” that Britain needed to be “bold” in confronting the challenges it faced.

Sunak became the ruling Conservatives’ new leader on Monday after triumphing over rival contender Penny Mordaunt who failed to secure enough nominations from Tory MPs, and ex-premier Boris Johnson who dramatically aborted a comeback attempt.

The 42-year-old Hindu is Britain’s first prime minister of colour and the youngest in more than two centuries. President Joe Biden called the choice “groundbreaking”.

Sunak was due to take power in a morning audience with King Charles III – who is anointing his first prime minister since ascending the throne following the death of his mother Queen Elizabeth II.

The new prime minister was then expected to speak at around 11:35 am (1035 GMT).

- ‘Unite or die’ -

Britain’s Conservative-supporting media hailed Sunak’s appointment.

“The force is with you, Rishi,” ran The Sun’s headline, in a reference to Sunak’s love of “Star Wars” films. The Daily Mail called it “a new dawn for Britain”.

But the left-leaning Guardian highlighted Sunak’s warning to Conservative MPs that the party must “unite or die”.

Truss left office as the shortest-serving premier in history, after a calamitous tax-slashing budget sparked economic and political turmoil.

The 47-year-old announced her resignation last Thursday, admitting she could not deliver her mandate from Conservative members – who had chosen her over Sunak in the summer.

He has now staged a stunning turnaround in political fortunes, and vowed to do the same for Britain as it confronts decades-high inflation, surging borrowing costs and imminent recession.

But he also faces the uphill task of uniting a party riven with divisions and infighting.

Gavin Williamson, who served as a minister in the Tory governments of both Theresa May and Johnson, said the party was in the “last chance saloon” on unity.

Iain Duncan Smith, a former Conservative leader, added that MPs now understood the “existential threat” facing the Tories and that they needed to unite or accept being “out of power for a long time”.

- ‘Choices’ -

After delivering the now all-too-familiar new leader’s speech, Sunak will start appointing his top team before facing his first session of “Prime Minister’s Questions” in parliament on Wednesday.

Finance minister Jeremy Hunt – appointed by Truss just 11 days ago in a bid to salvage her premiership – could remain in the role after stabilising the markets.

He endorsed Sunak on Sunday, writing in the Telegraph that he was a leader “willing to make the choices necessary for our long-term prosperity”.

After reversing almost all of Truss’s various tax cuts, Hunt has warned “difficult decisions” loom over public spending.

Whoever heads the Treasury is set to unveil the government’s much-anticipated fiscal plans on October 31.

Sunak must also decide whether to appoint to his cabinet senior MPs who did not support him, such as Mordaunt, in a bid to unify his fractured party.

One unlikely to get a seat around the table is former boss Johnson, who was driven out in July partly thanks to Sunak’s resignation.

On Sunday he announced he would not go forward with his audacious leadership bid.

- ‘No mandate’ -

Sunak, a wealthy descendant of immigrants from India and East Africa, is also facing calls for a general election after becoming the latest leader who lacks a direct mandate from the electorate.

Pollster Ipsos said Monday that 62 percent of voters want a vote by the end of the year.

“He has no mandate, no answers and no ideas,” Labour’s deputy leader Angela Rayner tweeted.

Ed Davey, leader of the Liberal Democrats, welcomed the country getting its first British Asian leader but also insisted it was time for a general election.

“Given the Conservatives have trashed the economy… I guess one’s not surprised that they’re scared of the British public,” he told Times Radio.

The next election is not due until January 2025 at the latest and opposition parties have no way to force one, unless dozens of Conservative MPs acquiesce.

That appears unlikely as a flurry of polls show Labour with its largest lead in decades.