Suella Braverman has criticised Liz Truss’s “tumultuous” premiership as she quit as home secretary, further imperilling the embattled Prime Minister’s grip on power.

The popular figure among the Tory right told Ms Truss she had made a “technical infringement” of the rules by sending an official document from a personal email and was now taking responsibility.

Ms Braverman is a figure-head of the right in the party and the exit of a former Tory leadership candidate will create further challenges for Ms Truss as she struggles to maintain her grip on power.

In her letter resigning as home secretary, Suella Braverman said she had “concerns about the direction of this government”.

“It is obvious to everyone that we are going through a tumultuous time,” she said.

“I have concerns about the direction of this government. Not only have we broken key pledges that were promised to our voters, but I have had serious concerns about this Government’s commitment to honouring manifesto commitments, such as reducing overall migration numbers and stopping illegal migration, particularly the dangerous small boats crossings.”

The Guardian, which first reported her departure, said that former transport secretary Grant Shapps, a major backer of Rishi Sunak for the Tory leadership and a critic of Ms Truss, was being lined up to succeed Ms Braverman.

The Sun reported that Ms Braverman was sacked, but this has not been confirmed officially.

Ms Braverman, a former attorney general, only became home secretary on September 6 when Ms Truss brought her in to replace Priti Patel.

Her tenure as home secretary has been controversial, having accused Tory critics who successfully forced Ms Truss into U-turning over plans to scrap the top rate of income tax of a “coup”.

Mr Shapps was one of the leading voices urging the Prime Minister to backtrack on the widely-criticised plan during the Tory party conference earlier this month.

Ms Braverman, a former attorney general, only became home secretary on September 6 when Ms Truss brought her in to replace Priti Patel.

Her tenure as home secretary has been controversial, having accused Tory critics who forced Ms Truss into U-turning over plans to scrap the top rate of income tax of a “coup”.

Mr Shapps was one of the leading voices urging the Prime Minister to scrap the plan during the Tory party conference earlier this month.

Earlier in the day, Ms Truss insisted she was a “fighter, not a quitter” as more Tory MPs heaped pressure on her to exit No 10.

She made a public apology in the Commons as she faced Prime Minister’s Questions for the first time since her economic plan was ditched by Chancellor Jeremy Hunt.

On Monday, Mr Hunt reversed almost all the tax cuts announced by predecessor Kwasi Kwarteng as he sought to calm financial markets following weeks of turbulence.

The Prime Minister told MPs: “I have been very clear that I am sorry and that I have made mistakes.”

But she added: “The right thing to do in those circumstances is to make changes, which I have made, and to get on with the job and deliver for the British people.”

The Prime Minister is battling to retain her position and has risked a fresh fight with Tory MPs by making a vote on a Labour motion on fracking a test of confidence in her administration.

Labour leader Sir Keir Starmer mocked Ms Truss, saying: “What’s the point of a Prime Minister whose promises don’t even last a week?”

He added of a book which is being written about her: “Apparently it’s going to be out by Christmas. Is that the release date or the title?”

In other developments, Ms Truss:

– Committed to the triple-lock on pensions, meaning the state pension will increase in line with the 10.1% inflation figure from April, after being threatened with a backbench revolt.

– Declined to give the same guarantee to link increases in benefits to inflation.

– Insisted she backed social care reform following a Times report that plans for a cap on costs was being delayed for a year.

Her own MPs posed some of the most challenging questions on issues including fracking, social care, international aid spending and the benefits increase, in a sign that there was little appetite to rally round the beleaguered leader.

But former Cabinet minister Sajid Javid – the subject of a hostile briefing from a No 10 source who described him as “shit” – did not ask a question, despite being listed to do so.

One of the Prime Minister’s senior aides, Jason Stein, has reportedly been suspended pending an investigation by the Cabinet Office propriety and ethics team into the briefing against Mr Javid.

Asked about the report, the Prime Minister’s press secretary said: “I am not going to get into individual staffing matters but the Prime Minister has made very clear to her team that some of the sort of briefings that we have seen are completely unacceptable about parliamentary colleagues and they must stop.”

Ms Truss is attempting to build bridges with Tory MPs, including through “fairly regular” events for backbenchers, No 10 said.

But there is speculation that the chairman of the Tory backbench 1922 Committee Sir Graham Brady had already received more than 54 letters calling for a confidence vote in the PM, the threshold for triggering one if Ms Truss was not in the 12 months’ grace period for new leaders.

“I wouldn’t get into private conversations,” the Prime Minister’s press secretary said.

“That’s the first I’ve heard.”

Tory MP William Wragg told the Commons he has submitted a letter to Sir Graham.

Mr Wragg, vice chairman of the 1922 Committee, told MPs: “What occurred with that financial statement, I am personally ashamed because I cannot go and face my constituents, look them in the eye and say that they should support our great party, and the polls would seem to bear that out.”

Conservative MP Steve Double warned Ms Truss will likely have to stand down “quite soon”, telling Times Radio that “she is absolutely in the last-chance saloon”.

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