Rishi Sunak is set to be officially appointed Prime Minister before noon tomorrow after he won the race to replace Liz Truss in No10.

The 42-year-old is due to travel to Buckingham Palace to meet King Charles tomorrow morning before making his first address to the nation as PM from Downing Street around 11.35am.

He today pledged to run No10 with ‘integrity and humility’ but warned of ‘profound challenges’ to come as he prepares to begin his premiership.

Mr Sunak delivered the stark message after being confirmed as the next PM when his sole remaining rival Penny Mordaunt failed to make the threshold of 100 nominations needed to trigger a run-off in the Tory leadership contest.

Speaking to a camera at Conservative HQ, Mr Sunak said the UK is a ‘great country’ and vowed to work ‘day in and day out’, but pointed to serious economic problems.

Outgoing PM Liz Truss is due to chair a last Cabinet meeting at 9am tomorrow before making a final address as premier outside No10. She will then travel to Buckingham Palace to formally offer her resignation to King Charles.

His Majesty will subsequently appoint Mr Sunak as PM, with the incoming premier set to make his own speech from Downing Street around 11.35am after travelling back from the Palace.

When Boris Johnson chaired his final Cabinet meeting in July, he was presented with Winston Churchill’s six-volume history on the Second World War following a whip-round among his top ministers.

Ms Truss will also be expected to recieve a gift from her senior team when she addresses them for the final time tomorrow, despite lasting just 44 days as PM before resigning.

Mr Sunak received a rapturous reception when he made a 10-minute private speech to MPs at Parliament this afternoon, telling his troops that leadership challengers Mr Johnson and Ms Mordaunt, as well as his former rival Ms Truss, were ‘all good Conservative colleagues and friends’. 

‘We’re united behind the policy and now cannot afford the indulgence of division over personality,’ he added.

According to one MP present he said: ‘We have one chance. It is unite or die.’

It marks a spectacular political revival for Mr Sunak, just seven weeks after he was soundly defeated by Ms Truss in the struggle to succeed Mr Johnson. But after her extraordinary 44-day implosion, he now faces one of the toughest in-trays for any PM with the public finances in chaos and the worst of the cost-of-living to come.

One of his first tasks will be to form a new Cabinet that can unite the warring party, with Jeremy Hunt set to continue as Chancellor – a week before he delivers a crucial Halloween Budget – and speculation that Ms Mordaunt could become Foreign Secretary. 

Ms Truss congratulated Mr Sunak on his ‘appointment’ this afternoon, saying he had her ‘full support’.