Pressure on embattled Culture Secretary Maria Miller has been ramped up by a poll suggesting a large majority of voters think she should be dropped from the Cabinet, stripped of her responsibility for press regulation and thrown out of the House of Commons.
Tory chairman Grant Shapps has called for a line to be drawn under the controversy over Mrs Miller's expenses, following her apology to the House of Commons on Thursday.
But the Survation poll for the Mail on Sunday found that almost three-quarters of voters (73%) thought her 32-second apology was inadequate, and similar numbers (75%) felt David Cameron was wrong to offer her his support.
Some 78% of those questioned said she should forfeit her Cabinet post as Culture Secretary, 66% said she should lose powers over press regulation and 68% said she should be "sacked" as an MP - something which is not currently possible, as the Government is yet to introduce the power of recall promised in the 2010 Coalition Agreement.
Meanwhile, the Sunday Telegraph quoted an unnamed "senior minister", speaking on condition of anonymity, as saying she should go: "In my view she has clearly behaved in a way that is incompatible with what she should be doing as a Cabinet minister. The decision to keep her on undermines the Prime Minister because he has talked about a new kind of politics."
Mrs Miller's apology came after a cross-party panel of MPs overruled Parliament's standards commissioner Kathryn Hudson, who recommended after an inquiry that the Culture Secretary should repay £45,000 in expenses for a house which she shared with her parents.
The Commons Standards Committee instead decided she needed to hand back just £5,800 and say sorry for failing to co-operate fully with the inquiry.
The watchdog in charge of MPs expenses said it was time for the House of Commons to give up the power to police itself over standards and ethics, warning that "MPs marking their own homework always ends in scandal."
Sir Ian Kennedy, chairman of the Independent Parliamentary Standards Authority told the Sunday Times: "We have made great progress in cleaning up the problems of the past. To avoid further damage to Parliament in the future, it should have the confidence to give away powers in regulating itself and see that independent regulation is the best, most transparent way forward.
"MPs marking their own homework always ends in scandal. It happened with expenses. It will happen with standards investigations too. Ipsa has shown that independent regulation of parliamentary behaviour can work. Our reforms have cleaned up the system."
MPs should "learn a lesson" from the independent system of regulation of expenses which was introduced in the way of the 2009 scandal and ensure that Ms Hudson too is "given the freedom to carry out her work and not have her wings clipped by MPs", said Sir Ian.
Letters released following Mrs Miller's apology revealed the Culture Secretary told Ms Hudson that it would be "irrational, perverse and unreasonable" to uphold the complaint against her and warned that she could go over her head to ask the MPs on the Standards Committee to intervene.
In another message, she wrote: "In light of the evidence that is before you ... to continue to regard this spurious complaint as a serious matter would give it credence it does not deserve and undermine the inquiry process in comparison to issues that really are serious matters."
John Mann, the Labour MP whose complaint sparked the Commissioner's investigation, said: "These emails show that Maria Miller bullied and threatened the independent commissioner."
But Mr Shapps said he believed Mrs Miller had just been "frustrated" at the long-drawn out inquiry.
The Tory chairman told Channel 4 News: "I don't want to get into the semantics of which words should have been used. The simple fact of the matter is that Maria has accepted in her statement to Parliament that this perhaps could have all been handled much faster.
"I'm sure she was frustrated that it hadn't been and that's why she said she of course unreservedly apologised.
"This has been now very thoroughly investigated in a huge amount of detail, every aspect of it. It's come to a conclusion... It's happened now, she's made an apology and the Prime Minister has said it draws a line under it, and that's of course what it does."
He also defended the Culture Secretary's special adviser Jo Hindley, who was caught on tape telling a reporter investigating the expenses story that she wanted to "flag up" the fact that Mrs Miller would be meeting her editor to discuss the Leveson inquiry into press ethics.
Despite the claim of then Telegraph editor Tony Gallagher that this amounted to a threat, Mr Shapps insisted that Leveson had been mentioned only in the context of the doorstepping of Mrs Miller's elderly father, who was ill at the time.
Mr Cameron has twice publicly voiced his support for the Culture Secretary, but yesterday omitted her from a list of several Cabinet ministers who he singled out for praise in a speech to the Conservative Spring Forum.
Deputy Prime Minister Nick Clegg declined to come to Mr Cameron's aid, saying: "All the issues to do with her position and indeed to do with the behaviour of her office, alleged or not, is entirely a matter for the Prime Minister."
And there was further embarrassment for Mrs Miller when a string of mocking messages was sent out on the Twitter feed of her own Department for Culture, Media and Sport.
The first bogus tweet from the @DCMS account said: "Seriously though guys which one of us hasn't embezzled and cheated the taxpayer?? #FreeMariaMiller".
It was swiftly followed by "@Maria_MillerMP is like a modern day Robin Hood, she robs the poor to help the rich" and then "Is @Maria_MillerMP guilty? We will let the public decide".
A spokeswoman from the DCMS confirmed the account had been hacked but said they had "absolutely no idea" who was responsible.
David Mellor, who resigned from John Major's Cabinet - where he held the same post as Mrs Miller - in 1992, told Sky News's Murnaghan show: "I don't think it matters whether she resigns or not. She won't be missed if she goes and she won't be noticed if she stays.
"What this is all about is first of all the judgement of David Cameron, and secondly the integrity of the British Parliament."
Work and Pensions Secretary Iain Duncan Smith has suggested that Ms Miller is undergoing a Tory backlash for having been the minister responsible for the same-sex marriage Bill.
As Equalities Minister, Ms Miller helped steer the Marriage (Same Sex Couples) Act 2013 Bill through the Commons, which has been hugely unpopular among many grassroots Tories.
Mr Duncan Smith suggested that that was a contributing factor in her fall in the polls.
Speaking on BBC One's The Andrew Marr Show, Mr Duncan Smith said of his former minister for disabled people: "I am enormously fond of her.
"I think she has done a very good job in a very difficult set of circumstances, with the Leveson Inquiry, which has stirred up a lot of media antipathy to her. And also the gay marriage stuff - there's a lot of Conservatives out there who perhaps weren't necessarily supportive, also feel rather bitter about that.
"In a sense, she is also receiving some of that (backlash) as part of this process."
He said he had always known her to be "a reasonable and honest person", but that ultimately whether her position was tenable or not was a matter for the Prime Minister.
"My view generally is that I'm supportive of Maria, because if we are not careful we end up with a witch hunt of somebody."
Asked if she should rethink her position, he replied: "No, I don't think so."
On the issue of IPSA's perceived lack of independence, he said it was "eating away at the credibility of Parliament" and that he was supportive of "whatever it takes to restore that credibility".
Former CBI director general, Lord Digby Jones of Birmingham, said Ms Miller should have been sacked, as her actions had not been "in the spirit" of Parliament.
Speaking on BBC Radio 5Live's Pienaar's Politics, he said: "In a company environment, in a business environment, you'd be asking for a resignation.
"Because if you have got the situation where, as I understand the matter, there is no problem with reclaiming the interest on the purchase of the house, it's the interest on the additional loans she then had after that, as I understand the matter. And if that's the case, it might be to the letter of the law, but it's not in the spirit of what it was about."
On the Tories' "women problem", the cross-bencher added: "I think it's an absolute legitimate motive to say, 'I need more women in my cabinet'. But I'm sure he (the Prime Minister) could have found another one, if you know what I mean."
Asked if Mrs Miller has his "100% support", Mr Shapps told Sky News's Murnaghan: "Yes, she does. Maria Miller is a very, very hard-working minister. She has accepted fully the recommendations of the committee without reservation, and she should be able to get on with her job, and the Prime Minister has said that's what he wants her to do."
In a separate interview with BBC Radio 5 Live's Pienaar's Politics, Mr Shapps was asked four times whether Mrs Miller had his backing, and stressed that it was an issue for the Prime Minister.
"I echo the words of the Prime Minister," he said.
"Ultimately this is a matter for him and for Maria and the PM has been clear that she has gone through this process, made the apology to the House and the PM is satisfied with that."
Pressed on whether she had his personal support, Mr Shapps replied: "Well, listen, I don't put her in the post... She is somebody who, let's face it, has worked on a lot of tricky sensitive issues.... Leveson being one of them. So she has a portfolio which has happened to have been particularly complicated.
"Yes, she has gone through a complete process. She has done exactly what the committee asked her to do... And the Prime Minister has been clear that he is then satisfied with that and so, of course, I am satisfied with it as well."
Mr Shapps said that the system under which a panel of MPs has the final say on standards complaints should be "looked at", but said it did not necessarily need reform.
He told Murnaghan: "I don't think that just because we didn't get the result that others might have wanted to see means that the system necessarily is wrong. But I do think it's right that the system should be looked at."
He added: "These things can always be looked at. It's worth noting though, that there are three lay members on that committee - people who are completely independent and not politicians, not MPs. They don't vote, it's true, but had they had something different to say, they were completely at liberty to produce a minority report and say they disagreed with the findings of the committee.
"These guys are the ones who have taken many months to look at the allegations, to throw them out, to dismiss them and to recommend that Maria apologises for the manner in which information was provided."
Labour shadow cabinet member Jim Murphy said that the Miller case had demonstrated the need for a "radical" overhaul of the system under which MPs pass judgment on their own colleagues.
He called on Mr Cameron to "get a grip" over standards and said that the Miller case showed that the Prime Minister had failed to ask his ministers tough questions.
Asked whether Mrs Miller should go, Mr Murphy told Sky News's Murnaghan: "In politics, it's often the cover-up that gets you. This might be the first example in modern times of the celebration being about to get you.
"The way she offered a 30-second apology and the way the Prime Minister seemed to celebrate the findings of that committee, led to people asking many more questions about what did Downing Street know and what did the whips know."
He added: "There is a bit of a pattern here of the Prime Minister not asking the hard questions. He didn't ask the hard questions when it came to Andy Coulson, he has not asked the hard questions on other ministerial issues and it's been left to the media and some backbench MPs to ask the tough questions that Downing Street and the Prime Minister really should be on top of.
"There is a sense of complacency when it comes to his relationship to these ministers.
"There is a wider point, which isn't about party politics, which is about the way in which politics is demeaned every time there are these sorts of scandals, which is why the Prime Minister has got to get a grip and why Parliament has got to modernise the committee which oversees these things."
Mr Murphy said that the modernisation of the Standards Committee was "the piece of the jigsaw that hasn't been completed" in the reforms of Parliament's rules following the expenses scandal of 2009.
"One of the things we have learnt from this is that the current rules on the way in which these sorts of things are overseen by the committee now have to change," he said.
"There needs to be a radical overhaul of the Standards Committee and the way these sorts of cases are dealt with in the future."