Home Secretary Suella Braverman has admitted sending official documents from her Government email to her personal address on six separate occasions.
As she battled to stay in her job, she detailed the timeline of events that led to her resigning her post on October 19 under former Prime Minister Liz Truss.
She was reinstated just six days later by Rishi Sunak, who she had backed for the Tory leadership, after assuring him that she "would no longer use personal IT for Government business".
Ms Braverman also requested briefing and guidance by "security experts on what constitutes appropriate use of Government and personal IT", she said in a letter to the Home Affairs Select Committee.
In the statement Ms Braverman said she "sent official documents from my Government email to my personal email address on six occasions".
Ms Braverman, dubbed ‘leaky sue’, emailed a draft written ministerial statement (WMS) on immigration policy to Conservative MP Sir John Hayes, using her personal email instead of her official government account.
The document made reference to high level policy on legal migration and proposals.
Ms Braverman had intended to copy in Sir John Hayes's wife, who works in his office, but accidentally sent it to a staff member of Conservative MP Andrew Percy.
She insisted it was not classified as secret or top secret but that some "sentences had not been fully agreed by all departments".
"The draft WMS did not contain any information relating to national security, the intelligence agencies, cyber security or law enforcement," she said.
"It did not contain details of any particular case work."
However Mr Percy sent her an email stating it was "not acceptable" to share documents via gmail.
"Simply asking my team to delete this email and ignore it is not an acceptable response to what appears, on the face of it, to be a potentially serious breach of security," the Brigg and Goole MP told her.
"I am considering a point of order on this issue and have raised it with the Chief Whip.
"You are nominally in charge of the security of this nation, we have received many warnings even as lowly backbenchers about cyber security."
Ms Braverman's actions breached the ministerial code in two sections, on following the advice about “security of Government Business” and on abiding by “collective responsibility”.
She admitted there was a security risk, but insisted it was "low".
"The breach was swiftly and proactively reported to officials, I nevertheless decided to take full responsibility by tendering my resignation," she added.
Labour and the Liberal Democrats had called for Ms Braverman to lay out any alleged security breaches that led to her being forced to resign and asked her to make an official statement in Parliament.
A Labour source said: "If the Home Secretary thinks this letter is the end of the matter then she grossly underestimates the seriousness of this conduct. There are now even more questions to be answered."
Lib Dem Chief Whip Wendy Chamberlain MP said: "This was not a one-off error, the Home Secretary has admitted breaking the rules on an industrial scale.
“Deliberately sending a sensitive government document to a friend without clearance is completely beyond the pale.
“If the Home Secretary wants to maintain even a shred of her dignity and credibility, she must resign now and apologise for her violations of the public’s trust.”
On Monday morning Shadow Home Secretary Yvette Copper told BBC Radio 4: "It's the Home Secretary, she's responsible for our national security, for public safety, for immensely important issues right across the country.
"It's her job. She's got to be able to do it and if she can't, and clearly that is what's happening at the moment because she can't answer those basic questions, and there's real issues about trust here, then she should not be doing this job."
The Prime Minister’s official spokesman said: “She has provided a detailed account around those issues, both the individual issue, forwarding that email and a further investigation.
“She has set out in quite a lot of detail what has happened, and mitigations that have been taken.
“As she makes clear, she made an error of judgement, she recognises that the approach she took was not right, and it was for those reasons that she felt it was right to resign.
“She has apologised both to the Prime Minister, to the MP involved, and she has set out details in the letter to the committee.”
