Suella Braverman has been replaced by Grant Shapps as home secretary in Liz Truss's government, after 43 days in post.
No.10 confirmed Shapps's appointment shortly after Braverman announced her departure this afternoon, less than a week after former chancellor Kwasi Kwarteng was sacked after last month’s mini-budget caused turmoil in the markets.
In a letter to the prime minister that Braverman shared on Twitter this afternoon, she said: "Earlier today I sent an official document from my personal email to a trusted parliamentary colleague as part of policy engagement and with the aim of garnering support for government policy on migration.
"This constitutes a technical infringement of the rules."
She added: "As soon as I realised my mistake, I rapidly reported this on official channels and informed the cabinet secretary.
"As home secretary, I hold myself to the highest standards and my resignation is the right thing to do."
Braverman's letter contained a thinly-veiled message to the under-pressure prime minister.
"Pretending we haven't made mistakes, carrying on as if everyone can't see that we have made them, and hoping that things will magically come right is not serious politics," she continued.
"The business of government relies upon people accepting responsibility for their mistakes."
"I have made a mistake, I accept responsibility, I resign."
There had been tension between Braverman and Truss ever since the former was appointed home secretary, with Braverman saying she had “reservations” about a proposed trade deal with India because it would increase immigration to the UK.
In a short letter of reply this evening, which distilled Braverman's achievements as home secretary to overseeing policing around mourning the Queen's death and work on the Northern Ireland Protocol, Truss said that she was "grateful" for her service. She implied that Braverman's conduct could have breached the ministerial code.
"It is important that the ministerial code is upheld, and that cabinet confidentiality is respected," Truss wrote.
Grant Shapps, a staunch ally of Truss's onetime leadership rival Rishi Sunak, was named as Braverman's successor at the Home Office by No.10 via Twitter just after 6pm.
Shapps, who supported the former chancellor in the party's leadership election, made clear his opposition to Truss and Kwarteng's policy of abolishing the top 45p rate of income tax before it was ditched earlier this month.
The move comes as Liz Truss battles on to try and save her premiership, with a vote this evening on fracking that government whips have said is being considered "a confidence vote in the government" and widespread unhappiness among backbenchers.
Braverman's departure was immediately followed by a mini rebellion over the vote. Former energy minister Chris Skidmore said that he would be willing to have the whip suspended for not supporting the government.
He was immediately followed by former ports minister Tracey Crouch, and Conservative MP for Guildford Angela Richardson.
Caitlin Doherty is a reporter for CSW's sister title PoliticsHome, where a version of this story first appeared