British Prime Minister Boris Johnson will face a vote of confidence by Conservative MPs this evening as discontent over the lockdown-busting parties in No 10 and the direction of his leadership reached a tipping point.

Mr Johnson was informed yesterday that he would face the vote after Graham Brady, the chairman of the backbench 1922 Committee, confirmed he had received the 54 letters from Conservative MPs needed to trigger the ballot.

The vote, by secret ballot, will take place at Westminster between 6pm and 8pm, with the count to take place immediately afterwards.

A steady stream of Conservative MPs called publicly for the prime minister to stand down in the wake of Sue Gray’s report into breaches of the Covid-19 regulations in No 10 and Whitehall.

In order to oust Mr Johnson, they will need 180 MPs, and allies of the prime minister made clear he is determined to fight to stay on.

Speaking shortly after Mr Brady made his announcement, Health Secretary Sajid Javid told Sky News: “If there is (a vote) the Prime Minister will stand and fight his corner with a very, very strong case.”

A No 10 spokeswoman said: “Tonight is a chance to end months of speculation and allow the Government to draw a line and move on, delivering on the people’s priorities.

“The PM welcomes the opportunity to make his case to MPs and will remind them that when they’re united and focused on the issues that matter to voters, there is no more formidable political force.”

Mr Brady said he had informed Mr Johnson yesterday that the threshold of 15% of the parliamentary party calling for a vote had been passed.

“I have followed the rules that we have in place. I notified the Prime Minister yesterday and we agreed the timetable for the confidence vote to take place,” he said.

“He shared my view, which is also in line with the rules that we have in place, that that vote should happen as soon as it could reasonably take place, and that would be today.”

He indicated some Conservative MPs had submitted letters post-dated until after the end of the Platinum Jubilee celebrations, which meant the contest would not clash with the extended bank holiday festivities.

In an indication of the anger felt on the Tory benches, former minister Jesse Norman – who had been a long-standing supporter of Mr Johnson – published a scathing letter to Mr Johnson withdrawing his support.

Mr Norman said the Gray report showed Mr Johnson “presided over a culture of casual law-breaking at 10 Downing Street” and “to describe yourself as ‘vindicated’ by the report is grotesque”.

Cabinet ministers rallied round Mr Johnson, including those who could seek to replace him if he is forced out.

Foreign Secretary Liz Truss said: “The Prime Minister has my 100% backing in today’s vote and I strongly encourage colleagues to support him.

“He has delivered on Covid recovery and supporting Ukraine in the face of Russian aggression. He has apologised for mistakes made. We must now focus on economic growth.”

Chancellor Rishi Sunak said: “The PM has shown the strong leadership our country needs”.

“I am backing him today and will continue to back him as we focus on growing the economy, tackling the cost of living and clearing the Covid backlogs,” Mr Sunak said.

Deputy Prime Minister Dominic Raab said: “The PM has got the big calls right – securing life-saving vaccines, firing up our economy and standing up to Putin’s aggression against Ukraine.

“We need to back him, unite and focus on delivering the people’s priorities.”

Mr Johnson’s chief of staff Steve Barclay, writing on the Conservative Home website, said the Government was working to address the country’s economic problems and to deliver the levelling-up agenda to reduce regional inequality.

“To disrupt that progress now would be inexcusable to many who lent their vote to us for the first time at the last general election, and who want to see our Prime Minister deliver the changes promised for their communities,” he said.