Rishi Sunak says he will try to “fix” the mess left by his predecessor after being officially appointed Britain’s new Prime Minister in a meeting with the King.

Standing outside his Downing Street office on Tuesday (local time), Mr Sunak paid tribute to Liz Truss but said she had made mistakes.

He also took aim at another predecessor, Boris Johnson, by saying the mandate the Conservatives were handed at the 2019 election was not the property of one individual.

“I want to pay tribute to my predecessor Liz Truss … Some mistakes were made. Not born of ill will or bad intentions. Quite the opposite in fact. But mistakes nonetheless,” he said.

“I have been elected as leader of my party and your Prime Minister, in part to fix them.

“That work begins immediately. I will place economic stability and confidence at the heart of this government’s agenda. This will mean difficult decisions to come.”

Tweet from @RoyalFamily

Mr Sunak wasted no time reshuffling his cabinet and immediately came under fire from the opposition for bringing back Suella Braverman. She resigned just last week for breaking the ministerial code.

Ms Braverman returns as Home Secretary six days after leaving the role. Jeremy Hunt will remain as Chancellor after he replaced Kwasi Kwarteng under Ms Truss.

Appealing to a public facing rising energy and food prices, Mr Sunak, one of the wealthiest lawmakers in parliament, said he fully appreciated how hard things were for many.

“All I can say is that I am not daunted. I know the high office I have accepted and I hope to live up to its demands,” he said.

“I stand here before you ready to lead our country into the future. To put your needs above politics, to reach out and build a government that represents the very best traditions of my party. Together we can achieve incredible things.”

Mr Johnson congratulated Sunak on his appointment as prime minister on Tuesday, urging Conservative Party colleagues to give him their full support.

“Congratulations to (Rishi Sunak) on this historic day, this is the moment for every Conservative to give our new PM their full and wholehearted support,” Mr Johnson wrote on Twitter.

Mr Sunak is Britain’s third PM in two months, tasked with tackling a mounting economic crisis, a warring political party and a deeply divided country in one of the greatest challenges to confront any new leader.

The 42-year-old former hedge fund boss was asked to form a government by the King on Tuesday. He will seek to bring an end to the infighting and feuding at Westminster that has horrified investors and alarmed international allies.

He addressed the nation from Downing Street before starting to build his cabinet of senior ministers.

Mr Sunak, one of the richest men in the British parliament, will have to find deep spending cuts to plug an estimated £40 billion ($72 billion) hole in Britain’s public finances due to an economic slowdown, higher borrowing costs and a six-month program of support for people’s energy bills.

With his party’s popularity in freefall, Mr Sunak will also face growing calls for an election if he moves too far from the policy manifesto that elected the Conservative Party in 2019. At the time, then leader Mr Johnson pledged to invest heavily in the country.

Economists and investors have said Mr Sunak’s appointment will calm markets, but they warn that he has few easy options when millions are battling a cost of living crunch.

“With a recession in 2023 now increasingly likely, and the next general election in only two years’ time, Rishi Sunak can expect a challenging premiership,” Eiko Sievert at the Scope ratings agency told Reuters.

Mr Sunak has warned his colleagues they face an “existential crisis” if they do not help to steer Britain through the surging inflation and record energy bills that are forcing many households and businesses to cut back spending.

“We now need stability and unity, and I will make it my utmost priority to bring our party and our country together,” he said as he was elected by Tory MPs on Monday.

Mr Sunak, Britain’s youngest prime minister for more than 200 years and its first leader of colour, replaced Ms Truss who resigned after 44 days following a “mini budget” that sparked turmoil in financial markets.

With debt interest costs rising and the outlook for the economy deteriorating, he will now need to review all spending, including on politically sensitive areas such as health, education, defence, welfare and pensions.

Speaking seven weeks to the day after she arrived as prime minister, Ms Truss gave a departure speech in front of 10 Downing Street. She did not apologise for her short tenure, and said she knew Britain was set for brighter days.

During Ms Truss’s brief time in office, the pound hit a record low against the US dollar, borrowing costs and mortgage rates surged, and the Bank of England was forced to intervene to protect pension funds from collapsing.

Investors will also want to know if Mr Sunak still plans to publish a new budget alongside borrowing and growth forecasts on October 31. That would help inform the Bank of England’s interest rate decision on November 3.

While many expressed relief that the Conservatives had settled on a new leader quickly, a sense of distrust remains among some voters. Others questioned whether struggling families would relate, or ever vote, for a multimillionaire.

“I think this decision sinks us as a party for the next election,” one Conservative MP told Reuters on condition of anonymity.

Mr Sunak, a Hindu, is also Britain’s first prime minister of Indian origin.

-with AAP