Former finance minister Rishi Sunak’s campaign to replace Boris Johnson as Prime Minister of the United Kingdom suffered another blow on Friday, as a key Cabinet backer of his jumped ship and switched his support to frontrunner Liz Truss.

Though Rishi Sunak was considered the early favourite to become the next Prime Minister, securing the backing of most Members of Parliament (MPs) in the first stage of the Tory leadership selection process, his support within the ranks of the parliamentary party has so far failed to translate to the Conservative party’s membership at large, who will have the final say on who will be the next inhabitant of Number 10 Downing Street next month.

Perhaps signalling the sinking ship feeling among Sunak supporters, one of the former Chancellor of the Exchequer’s top supporters from the Johnson administration, Welsh Secretary Robert Buckland, withdrew his support from Sunak on Friday.

“I have looked at ideas and principles first, and personalities second. During the parliamentary rounds, I backed Rishi Sunak as I felt that he was at that stage embodying what we needed,” Buckland wrote in The Telegraph.

“As the campaign has moved on, and as I have listened carefully to both candidates, I have thought deeply about the issues that move me and what I want to see the next prime minister doing. Changing your mind on an issue like this is not an easy thing to do, but I have decided that Liz Truss is the right person to take our country forward.”

The central debate to date in the contest between Truss and Sunak has been the issue of the cost of living crisis and the level of taxation in Britain, which rose to the highest level during Sunak’s tenure as the de facto head of the Treasury.

Sunak has justified the high level of taxes by saying that it is necessary to pay off the enormous debt accrued during the lockdowns when his department spent billions to pay people to stay at home and businesses to remain shuttered.

While Sunak has claimed to support lower taxes in principle, he has argued that it would be fiscally irresponsible to make any cuts during the high levels of inflation. Sunak’s alleged concern over inflation was, however, undercut by his promise this week to spend an additional £10 billion to help households deal with the rising cost of energy, as well as his history of green agenda spending.

In addition to Sunak — one of the richest men in the House of Commons through his marriage to an Indian industrial heiress — being seen as un-conservative on taxation and spending, he has also been unable to shake the label of Boris Johnson’s Brutus, with his resignation, alongside former Health Secretary Sajid Javid’s, ultimately sparking a wave of ministerial rebellions that forced Mr Johnson to announce his resignation.

Foreign Secretary Liz Truss, on the other hand, remained loyal to Johnson, at least in public, and despite her past as a Liberal Democrat and a Remainer in the Brexit referendum she has attempted to cast herself as the heir to the conservative governing philosophy of the late Prime Minister Margaret Thatcher. Truss has said that she would immediately seek to implement tax relief for the public upon gaining power.

For this, and her apparently tough stance towards the woke movement, Truss has garnered support from the right of the Tory Party, including from former leader Sir Iain Duncan Smith, Attorney-General Suella Braverman, and Brexit champion Jacob Rees-Mogg.

In an interview with GB News on Saturday, Mr Rees-Mogg said that he has thrown his support behind Truss because “she has been a real free market Conservative; she set up the free enterprise group among Members of Parliament to campaign for proper conservative economic policy, and therefore I am confident that she will challenge the Treasury orthodoxy to get us an economic policy that is actually in favour of growth.”

The Cabinet minister went on to say that while Truss had backed Remain in the 2016 referendum, she has since become an “enthusiastic” supporter of Brexit and that, besides Prime Minister Johnson, she, “was my greatest supporter in getting Brexit opportunities in the Cabinet committee that she chaired where other people were opposing them.”

Others, including Brexit leader Nigel Farage, have been less glowing in their appraisal of the Foreign Secretary, with Mr Farage warning that Truss will be nothing more than “Theresa May 2.0” and raising doubts over whether she will take the hardline approach needed with the European Union to fulfil the promises of Brexit and to solve the migrant crisis in the English Channel.

Follow Kurt Zindulka on Twitter here @KurtZindulka