Rishi Sunak suffered a setback on Saturday in his campaign to be elected as the Conservative Party leader and the Prime Minister of the United Kingdom as a former candidate for the post endorsed his rival Liz Truss.

Tom Tugendhat, who was in the initial shortlist before being knocked out of the race to become UK PM, on Saturday said he preferred Truss' campaign pitch with its promise of immediate tax cuts.?

Tom is a Conservative Party backbencher and the Chair of the Commons Foreign Affairs Committee. He is also a former soldier in the British Army.?

He said "only one has convinced me she's ready" after watching the candidates go head-to-head in live TV debates.

"Liz has always stood up for British values at home, and abroad. With her at the helm, I have no doubt that we will move with determination to make this country safer and more secure," wrote Tom in The Times newspaper.

He said both Truss and Sunak have "huge qualities and many talents" but Truss has an advantage on the world stage because of her Cabinet position. She is currently the Foreign Secretary.?

He wrote, "As foreign secretary, Liz is starting with a huge advantage. She can make our voice count."

Tom's endorsement of Truss follows the endorsement of another Conservative Party heavyweight Defence Secretary Ben Wallace. He described her as "authentic, honest and experienced".

Sunak was initially the frontrunner in the race in the ballots of his party colleagues, winning the most support from MPs in the first few rounds of voting. But since then, polling among the Conservative Party membership that will vote for the winner has shown Truss is more popular.

According to another report in The Times, even Sunak's former boss Boris Johnson is feeling sorry for him. He told friends he did not think that Sunak, the man he blames for his downfall, was going to make it.

"He almost feels sorry for him," a friend of Johnson’s was quoted as saying.

"[Rishi] got in with a crowd of malcontents who used him as part of their vendetta against Boris. What future is there for him now?" it said.

Sunak and Truss are next scheduled to go head-to-head in the TV debate on Thursday, when the first postal ballot papers will start landing at Conservative Party members' addresses.?

(With PTI inputs)