But the most bitter blow to Mr Sunak came on Thursday, when his erstwhile ally Sajid Javid – the former health secretary who resigned from Mr Johnson’s cabinet on the same day as the chancellor, precipitating the leadership crisis – also came out for Ms Truss.

In an article for The Times, Mr Javid said Ms Truss embodied the best instincts of both former British Conservative prime minister Margaret Thatcher – “clear-headed, fiscally disciplined” – and former Republican US president Ronald Reagan – “freedom-loving, sunny and optimistic”.

Ms Truss has explicitly rejected fiscal discipline, pledging more than £80 billion ($140 billion) of largely debt-funded tax cuts.

Mr Sunak has argued that this risks spurring inflation and leaving Britain with crippling interest bills. But Mr Javid, who is a former chancellor and fiscal hawk, sided with Ms Truss.

“There are no risk-free options in government. However, in my view, not cutting taxes carries an even greater risk,” he said.

“The circumstances we are now in require a new approach. Over the long term we are more likely to be fiscally sustainable by improving trend growth.”

Sunak fights on

After a stuttering start to her leadership campaign, commentators suggest Ms Truss has visibly grown in poise and confidence.

Mr Sunak is fighting gamely on – the two candidates are touring the country, appearing at hustings events in front of hundreds and even thousands of Conservative Party members – but the contest increasingly recalls the one-sided fight between Mr Johnson and his centrist rival Jeremy Hunt in mid-2019.

“It is very hard to see how Sunak recovers in the month or so between the opening and closing [of the membership ballot],” ConservativeHome editor Paul Goodman wrote as he released the site’s polling result.

“The Tory membership divides right-of-party-centre to left-of-party-centre by about two to one. And so, all other things being equal, the leadership candidate perceived to be more right-wing than the other will win by a margin of about two to one.”

Pundits are now penning articles warning Ms Truss’s opponents to take seriously the threat she might pose to them.

“If Labour think Liz Truss will be a walkover, they should think again. When the dust clears, they will be facing a formidable opponent,” said John McTernan, a former adviser to prime ministers Tony Blair and Julia Gillard, on the website Unherd.

“Her speaking style is clear and simple. The listener readily understands what she thinks and believes. Her opponents who too readily dismiss her as simplistic are missing the point. … The messages and policies that win are those that connect with the heart as much as the head.”

Right-wing Daily Telegraph columnist Allister Heath on Thursday wrote that her opponents would “rue the day they so completely underestimated her”.

Speculation is already starting to turn towards likely members of Ms Truss’s frontbench.

The early churn of the rumour mill suggests she will appoint suave business secretary Kwasi Kwarteng as chancellor, although others claim she might install one of her closest allies, the less impressive work and pensions secretary Therese Coffey.

One of her chancellor’s early tasks would be to review the Bank of England’s mandate, which is based around a 2 per cent inflation target.

“The best way of dealing with inflation is monetary policy, and … I want to change the Bank of England’s mandate to make sure in the future it matches some of the most effective central banks in the world at controlling inflation,” she told a hustings on Wednesday (Thursday AEST).

“The last time the mandate was looked at was in 1997. … Things are very, very different now.”