UK Interior Minister Suella Braverman tendered her resignation after controversy emerged over her sending an official document from her personal email in a "technical infringement" of government rules.
"I have made a mistake, I accept responsibility; I resign," she said in letter to Prime Minister Liz Truss posted on Twitter.
"It is obvious to everyone that we are going through a tumultuous time," Braverman wrote. "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."
After Braverman's former Transport Minister Grant Shapps was named new Interior Minister.
Second major resignation in one week
Braverman is the second senior minister to leave Truss' cabinet is less than a week, and was seen as another sign that the prime minister is struggling to stay in power after only six weeks in office.
On Friday, ex-finance minister Kwasi Kwarteng stepped down following outrage over proposed tax cuts that had sent the value of the pound plummeting and pushed already-soaring inflation to a 40-year high. He was replaced by Jeremy Hunt.
Earlier on Wednesday, Truss was hammered in parliament by MPs on her tax cut U-turn.
"I have been very clear that I am sorry, and I have made mistakes," she said, but added that she had no plans to resign.
After former Prime Minister Boris Johnson resigned in August, Braverman had competed alongside Truss for leadership of the Conservative party. Following her loss, she threw her support behind the prime minister.
While in office, she provoked criticism after she said it was her "dream" to follow through on her predecessor Priti Patel's controversial plan to send asylum seekers who arrive in the UK to Rwanda.
