Suella Braverman has dramatically resigned as Home Secretary after admitting sending an official document from her personal email.
In another blow to Liz Truss's embattled government, the ex-Cabinet minister said in a letter "it is right for me to go" and accepted responsibility for "a mistake".
It is understood the Cabinet Secretary Simon Case found two breaches of the ministerial code, including using a personal email and sending sensitive information to someone outside government.
Ms Braverman also took a departing shot at the Prime Minister and revealed she had "concerns about the direction of this government" after days of extraordinary turmoil.
Ms Braverman said: "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"
The former Cabinet minister added: "Pretending we haven't made mistakes, carrying on as if everyone can't see we have made them and hoping that things will magically come right is not serious politics.
In a short response to Ms Braverman, the Prime Minister praised her work at the Home Office, but said: "I accept your resignation and respect the decision you have made.
"It is important that the Ministerial Code is upheld, and the Cabinet confidentiality is respected".
Around an hour after her resignation, No10 also announced Ms Braverman had been replaced by the ex-transport secretary Grant Shapps - an ally of Rishi Sunak.
The extraordinary development means Ms Truss has lost both her Chancellor Kwasi Kwarteng and her Home Secretary in the first 50 days of her administration.
It came after the Prime Minister also cancelled a planned visit to Hertfordshire, with No10 failing to give a specific explanation beyond "government business".
Shadow Home Secretary Yvette Cooper demanded Ms Truss be summoned to the House of Commons to answer questions over the departure.
“The Home Secretary has been sacked or resigned this afternoon. This is utter chaos,” she said in Parliament. “This is no way to run a government.”
Ms Braverman, 42, is a figure-head of the right of the Conservative Party and ran unsuccessfully to replace Boris Johnson as leader in the summer.
She stood on a ticket of “shrinking the size of the state”, “getting rid of all this woke rubbish” including gender-inclusive language, and suspending Net Zero commitments.
Ms Braverman was the only leadership candidate who wanted to leave the European Convention on Human Rights.
She has attacked the “rights culture” that began under Tony Blair, and said schools do not have to use trans children’s preferred pronouns.
And she attacked people for “choosing to rely on benefits” despite more than four in every 10 Universal Credit claimants having a job.
The former Attorney General was only became Home Secretary on September 6 when Ms Truss brought her in to replace Priti Patel in a Cabinet of a loyalists.
Just yesterday she used a Commons appearance to launch a bizzare attack on "a "Tofu-eating wokerati" and a "coalition of chaos" - prompting laughter from the Labour benches.
Her exit from Government will create further challenges for Ms Truss's leadership after days of turmoil in Downing Street.
On Wednesday the Tory MP William Wragg became the sixth backbencher to publicly call for the Prime Minister to quit.
He told the Commons he was "personally ashamed" at the actions of the Government and had submitted a letter of no confidence to the chairman of the 1922 Committee, Sir Graham Brady.
Liberal Democrat Home Affairs Spokesperson, Alistair Carmichael said: “This is a Government in chaos.
"People should not be forced to watch the Conservative party implode day after day while real people suffer.
“There is a of cost of living catastrophe, health service crisis and now a rudderless home office.
“The only solution now is a General Election so the public can get off this carousel of Conservative chaos.”
Suella Braverman's resignation letter in full
"It is with the greatest regret that I am choosing to tender my resignation.
"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.
"As you know. the document was a draft Written Ministerial Statement about migration, due for publication imminently.
"Much of it had already been briefed to MPs.
"Nevertheless it is right for me to go.
"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.
"The business of government relies upon people accepting responsibility for their mistakes. 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.
"I have made a mistake: I accept responsibility: I resign.
"It is obvious to everyone that we are going through a tumultuous time. 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.
"It has been a great honour to serve at the Home Office. In even the brief time that I have been here. it has been very clear that there is much to do, in terms of delivering on the priorities of the British people.
"They deserve policing they can respect, an immigration policy they want and voted for in such unambiguous numbers at the last election, and laws which serve the public good, and not the interests of selfish protestors.
"I am very grateful to all of my officials, special advisers and ministerial team for all of their help during my time as I Home Secretary.
"I especially would like to pay tribute to the heroic policemen and women and all those who work at Border Force and in our security services.
"To oversee Operation Bridges - the largest policing operation in a generation - was a great honour and I am grateful to have had the opportunity to serve.
"I wish my successor good luck. Yours sincerely,
Rt Hon Suella Btraverman KC MP"
