Maria Miller has admitted she "let people down" as she struggles to cling on to her Cabinet job amid a growing Tory backlash.
The Culture Secretary broke her silence after nearly a week of dire headlines to insist she is "devastated" about the criticism she received from the Standards Committee.
In an article for local paper the Basingstoke Gazette, Mrs Miller said the last 16 months had been "difficult".
"I have unreservedly apologised for the way I handled and approached the inquiry," the MP wrote.
" I am devastated that this has happened, and that I have let you down."
With more Conservatives breaking ranks to express concern about David Cameron's determination to cling on to his minister, allies launched a furious counter-attack accusing the press of a "witch-hunt" because of her role in shaping a new regulatory system.
Mrs Miller's parliamentary aide Mary MacLeod texted colleagues asking them to speak up in her boss's favour, before touring broadcast studios.
"In some of the newspapers it has been like a witch hunt where they don't like the work that Maria has done on Leveson and gay marriage," she told Sky News.
"Therefore what they are trying to do is to find a way to get her out of the job."
In her article, Mrs Miller again insisted that the committee had dismissed "all allegations against me".
But she made no reference to independent standards commissioner Kathryn Hudson - who recommended she repay £45,000 but was overruled by the cross-party group of MPs, which reduced the sum to £5,800.
"Separately, I have already apologised and repaid an over-claim of my expenses, having myself drawn the committee's attention to the matter immediately I was aware of it," Mrs Miller wrote.
The minister is looking increasingly isolated, with the Prime Minister likely to face questions on the row in the Commons tomorrow and later at a meeting of the Tory backbench 1922 committee.
Former Commons speaker Baroness Boothroyd said Mrs Miller should quit "as a matter of honour" because of the damage she had done to Parliament.
"She is bringing Parliament into disrepute," Lady Boothroyd said. "I think the vast majority of people in this country, if they were asked, would have the same feelings that I have."
The furious peer - a Labour MP before becoming Speaker - said she was "outraged" at the way Parliament had been treated by Mrs Miller.
"I am annoyed, I am very angry. I love Parliament, I have cherished it, I have tried to develop it," she said.
"I feel somewhat outraged that people treat it in this way, quite frankly".
Parliament had been trying to repair the damage done by the expenses scandal in recent years and "this does not help at all", the peer told BBC Radio 4's PM.
She said: "I think it is a matter of honour, a question of honour, quite honestly. People in the past, leading members of government, leading Members of Parliaments have resigned. I think it is for Mrs Miller to have done likewise. I'm sad to say that I regard it as an error of judgment on the part of the Prime Minister that he didn't quietly say to her 'I think it is time to go, thank you for your services, but I think it is time to go'."
Anxiety on the Tory benches has focused on Mrs Miller's "perfunctory" 32-second apology on the floor of the House last Wednesday and her obstructive approach to the commissioner's inquiry.
There are fears the row could reignite public anger over expenses and undermine the party's prospects in forthcoming local and European elections.
Mrs Miller's article in the Gazette was 178 words long, compared to the 79 words in her apology to the Commons.
Tory MP Mark Field told BBC Radio 4's the World at One: "There is this whole public perception here that, rightly or wrongly, the Standards Committee as it is currently constituted is somehow open to being nobbled by senior Government members. In many ways it is that public perception that is so damaging here.
"It led to what many people regard to be an unacceptably perfunctory apology from Maria Miller. The important thing now is that we try and regain trust and it's very clear that the current system of having the Standards Committee, it is now unfit for purpose."
Another Conservative, Zac Goldsmith, expressed surprise that Mrs Miller was still in her job.
"It would be the Prime Minister's decision who he surrounds himself with. I am surprised that Maria Miller hasn't stepped down," he told BBC Radio 5 Live's Victoria Derbyshire show.
"This is a decision for her to make or it is a decision for David Cameron to make."
Fellow Tory MP Philip Davies said the continuing row over Mrs Miller was "extremely damaging" for the Conservative Party and needed to be resolved as soon as possible.
"Whether she resigns is a matter for her but obviously the whole thing is extremely damaging for the Conservative Party, it's damaging for Parliament as a whole and politicians - we all get tarnished by the same brush," he told BBC2's Daily Politics.
"It's damaging for the Government, for the Prime Minister. The sooner the matter is resolved, the better."
Yesterday work and pensions minister Esther McVey distanced herself from Mrs Miller, saying "it wouldn't be how I would have made an apology". And backbencher Jackie Doyle-Price, whose Thurrock seat is one of the most marginal in the country, said Mrs Miller should not expect colleagues to speak out in her favour.
Labour leader Ed Miliband also sought to increase the pressure, warning that the Prime Minister had serious questions to answer.
"He's got serious questions to answer about Maria Miller's failure to co-operate with the initial inquiry," he said in his first public comments on the issue.
"The ball is in his court - he's got to answer those questions about her status in the Government."
Pressure for reform at Westminster was strengthened after the three outside members of the Standards Committee - brought in to improve the way MPs are held to account - called for a "fundamental rewrite" of the existing code of conduct.
The three lay members complained that the issue was not taken seriously enough - with some committee meetings having to be abandoned because no MPs turned up - while the system allowed politicians to "ignore the spirit of the law".
But despite the PM's declaration yesterday that he was open to further reform, the Leader of the Commons Andrew Lansley warned MPs that making the standards watchdog fully independent would compromise parliamentary privilege and make the job harder to do.
Dozens of petitions calling for Mrs Miller to resign have been rejected from the official government website.
The e-petitions site lists around 60 proposed titles appealing for people to condemn the minister, but gives various reason why they cannot be hosted - including that it is a "party political" issue and a matter for the parliamentary authorities.
Labour MP Ian Mearns told the Morning Star newspaper: "It seems disgraceful in a democracy that over 60 petitions have been blocked. There should be an opportunity for people to voice their concerns."
A petition on the change.org website urging Mrs Miller repay £45,000 or quit has now attracted nearly 180,000 signatures.
Leader of the Commons Andrew Lansley was asked on the BBC's Newsnight programme whether he thought Mrs Miller would resign. "I don't think so. I hope not," he said. "From my point of view I think she is a good culture secretary."
Mr Lansley said it was the "Prime Minister's prerogative whether a minister has his confidence". He argued that the committee's report did not "disclose any dishonesty", but conceded that the MPs had "differed" with the standards commissioner on the "interpretation of the rules".
Pressed on how long he thought Mrs Miller would stay in her job, he replied: "I think that is an unreasonable question to ask."
Mr Lansley said he wanted to see a "simpler" code of conduct for MPs, but things had already changed since the scandal of 2009 and the public could have "confidence".