Boris Johnson is expected to warn Theresa May that Labour will win the next election unless she injects an extra £5bn into the NHS, at a showdown Cabinet meeting.

The Foreign Secretary will spark accusations that he is “on manoeuvres” by seizing centre stage to demand the Prime Minister act on widespread calls for an immediate health service bailout.

Cabinet members will be asked to back Mr Johnson’s plea for a £100m-a-week funding increase – still far short of the £350m-a-week he promised, notoriously, during the Brexit referendum.

Other Brexiteer ministers, including Michael Gove, Chris Grayling and Penny Mordaunt are likely to back him. Jeremy Hunt, the Health Secretary, has already gone public on the desperate need for more NHS cash.

Mr Johnson will warn Mrs May that she is making a fatal mistake if she fails to take on Labour on the crucial battleground of the NHS and make it her top funding priority.

However, the full-frontal challenge – far from his brief of foreign affairs – will trigger suspicions that he is preparing the ground for a future challenge against the Prime Minister.

Since surviving demotion in this month’s botched reshuffle, an emboldened Mr Johnson has grabbed the headlines with his proposal for a 26-kilometre road bridge to France.

He is also believed to be poised to make a key speech on the positive case for a “liberal Brexit” – having made known that he will not accept any drift away from a clean break from the EU.

But Ben Bradshaw, a supporter of the pro-EU Open Britain campaign, said “few ministers in modern history have done more to undermine our NHS than Boris Johnson”.

“His lies about how Brexit would deliver £350m a week for the health service have fatally damaged public trust,” Mr Bradshaw said.

“And the reality of Brexit so far has been a weakened health service with fewer resources and a Brexodus of nurses and doctors. Brexit is today the biggest threat facing the NHS.”

At the Cabinet meeting, Mr Johnson is not expected to refer to his referendum campaign, but will frame the NHS debate in terms of the need to defeat Mr Corbyn.

A suggestion by Mrs May's chief of staff, Gavin Barwell, that the Tories cannot hope to outfight Labour on the NHS, and should target other areas instead, has riled many Conservatives.

“Boris believes that if the Tories are going to beat Corbyn they must make the NHS a top priority and deliver new funding,” an ally told The Times.

“Every poll conducted shows the NHS is top of swing voter concerns and every expert says it needs more money. The Cabinet will have to act and the sooner the better.

“This isn't about the referendum - it's about delivering on the number one concern for the public.”

Nevertheless, Mr Johnson’s high-profile intervention is likely to anger the Prime Minister, who is already under fire from some of own MPs for lacking ideas and ambition.