David Cameron has opened the door to tougher regulation of MPs as he was again forced to defend his Culture Secretary over her expenses.
With the row over Maria Miller's mortgage claims showing little sign of dying down, the Prime Minister said he was ready to look at reforming the policing of politicians' behaviour.
The Commons Standards Committee has come in for fierce criticism since overruling an independent report that recommended Mrs Miller repay £45,000.
Instead, the cross-party body ordered her to say sorry and hand back just £5,800 - sparking accusations that MPs were still "marking their own homework".
Anxiety has been increasing among Tories over the fallout from the affair, while Labour upped the pressure by making a formal complaint about Mrs Miller's "contemptuous" 32-second apology to the House last week.
The Cabinet minister has also been forced to deny she will seek to dodge a capital gains tax (CGT) bill potentially running into tens of thousands of pounds after making a £1.2 million profit on the sale of her part-taxpayer-funded London home.
Mrs Miller bought the five-bedroom terrace property for £234,000 in 1996, and claimed around £90,000 in running costs over four years - almost the maximum allowed - after being elected to Parliament in 2005.
Parliamentary standards commissioner Kathryn Hudson concluded she should instead have designated it as her main home, and received expenses in her Basingstoke constituency.
A spokeswoman for the MP made clear she would tell HM Revenue and Customs that the London home - sold for just under £1.5 million in February - was not her primary residence between 2005 and 2009.
"HMRC will present her with a bill," the spokeswoman said. "There is no hiding anything here."
Profits on the sale of a main home are generally exempt from CGT, but the taxman will calculate a liability based on any periods in which the property was used as a second residence.
Based on the £1.2 million profit, the four years in which Mrs Miller claimed expenses against the house could leave her owing around £70,000.
The spokeswoman said: "The sale of the Wimbledon property in February falls in a tax year that has not yet been assessed.
"She will, of course, deal with the matter in accordance with HM Revenue and Customs rules and pay any tax that is due."
During a visit to Asda in Clapham, south London, Mr Cameron was asked about polling which showed most Conservatives believed Mrs Miller should be out of a job.
"What matters is doing the right thing. I think Maria has done the right thing by repaying the money, making an apology and now getting on with her job," he said.
Pressed on whether Mrs Miller was still in her post because she was a state-educated woman, he replied: "Maria Miller is in her job because she is doing a good job as Culture Secretary."
Mr Cameron stressed that regulation of expenses had been handed to the Independent Parliamentary Standards Authority.
He hinted that reforms could be taken further amid concerns about the operation of the Standards Committee.
"If there are further changes that people think are appropriate, I'm very open to suggestions," he said.
Tory backbenchers have been privately expressing irritation that the row is disrupting the local and European election campaign, and preventing the party from taking full advantage of improving economic conditions.
One ministerial aide, Nicola Blackwood, said Mrs Miller had "most serious" questions to answer and her response should be "clearer".
"The questions which she is being faced with are of the most serious and I have to say when I deal with my expenses, I am as transparent as I can be, it's all up on my website," she told BBC Radio Oxford.
"I have to say if I was faced with the kind of questions that she is faced with, I would be really quite worried indeed.
"I only know what has been reported in the papers ... but clearly it's very unhelpful for this to drag on in the way that it is."
Asked about Mrs Miller's response to the controversy, she added: "It would be helpful if it was clearer."
Labour backbencher Sheila Gilmore has lodged a formal complaint about the way Mrs Miller apologised for failing to co-operate fully with Ms Hudson's investigation.
"This was inadequate to the point of being contemptuous of your committee's report and the members' code of conduct," she wrote in a letter to Standards Committee chairman Kevin Barron.
Speaker John Bercow refused to allow an urgent question from another Opposition MP, John Mann, on reform of the committee.
Mr Mann - whose complaint originally triggered the inquiry into Mrs Miller - said the body had "no credibility whatsoever".
"The general public is pretty much unanimous, if not totally unanimous, that MPs should not sit in judgment on themselves. I totally agree," he said.
"The longer Parliament delays sorting this out, the worse it is for our democracy and the institution of Parliament."
But Attorney General Dominic Grieve warned of "constitutional issues" in changing the system.
"There has always been a tension between maintaining Parliament's independence and placing it under somebody else's scrutiny," he told BBC Radio 4's The World At One.
"I don't think that it needs me to explain that there is quite an interesting constitutional issue here. It's one which I think we've been wrestling with.
"In setting up Ipsa, Parliament moved very substantially away from the earlier model of its regulation. It's very much a matter for my parliamentary colleagues if they think that further change is going to be needed.
"I think that we need to evaluate that further change probably on how the system is working today, and not necessarily with reference to events that are 10 years old."
A petition on the change.org website calling on Mrs Miller to repay £45,000 or resign has attracted more than 100,000 supporters.
The Standards Committee is due to hold its first meeting since the report was published tomorrow morning.
Asked about her party colleague's apology, employment minister Esther McVey said: "I can honestly say it wouldn't be how I would have made an apology. But different people have different styles and do things in different ways."
She told ITV's The Agenda: "Fundamentally what we've got to do is make sure the public believe in their representatives and it is only right for the public and for politics that we get this matter right and we did actually because we changed the system in 2010."
The Prime Minister " has the final say" on whether Mrs Miller should keep her job, she said.
"He's standing by her. The whole system has changed since 2010 and remember this is pre-2010 - this couldn't happen now."
A group of senior Conservative activists said the PM's "irrational" decision to keep Mrs Miller in post was damaging both him and the party after a poll found more than two in three Tory supporters (69%) were among the 74% of voters who think he should have sacked her.
Only 8% backed the PM's decision.
The ComRes poll also found strong public support (65%) for removing the committee's right to alter the commissioner's recommended sanctions.
It was commissioned by Conservative Grassroots, an organisation founded by senior party activists which has mobilised local anger.
Chairman Robert Woollard, a former constituency party chairman, said: " Mr Cameron's support of the Culture Secretary is completely irrational.
"She has clearly broken the rules on MPs' expenses and according to media reports she and her allies have allegedly tried to bully and intimidate both the independent Parliamentary Commissioner for Standards and journalists who investigated her behaviour.
"When David Cameron spoke about the need for the actions of those in Parliament to pass the smell test, it was exactly for such occasions as these. Well this whole issue stinks and as this poll finds, it is incredibly damaging to our Party and the PM personally."
He said that while he had " huge personal sympathy" for Mrs Miller, elected representatives had to set an example, doubly so for ministers.
"Mr Cameron's and Mrs Miller's conduct so far falls way short of this ideal," he said.
The poll found 23% said they were more likely to vote Tory if more working class MPs from outside London were promoted, 30% among young voters aged 18-24.
"Given the clear perception problem that Mr Cameron surrounds himself by a handful of people from Eton and is unwilling to appoint solely on merit, replacing the Culture Secretary provides him with an opportunity that could boost our hopes at next month's European elections," Mr Woollard said.
"But inexplicably he continues to cling onto the Culture Secretary, which gives Nigel Farage a golden opportunity to take yet more votes from our party", he said.
ComRes interviewed 2,034 British adults between the April 4-6.