Former Conservative chairman Lord Tebbit has become the most senior Conservative to call for Maria Miller to resign as Culture Secretary, amid controversy over her response to an investigation into her expenses claims.
Lord Tebbit said that the Culture Secretary's "arrogant" handling of the scandal had revived voter anger over MPs' expenses and undermined the Government's message that "we're all in it together", adding: "The best way out of this is for Mrs Miller to resign."
His call came as Labour promised to reform Parliament's standards system in the wake of controversy over the decision of a panel of MPs to overrule a watchdog's judgment on Mrs Miller.
Pressure on the Culture Secretary has been heightened by a poll suggesting that 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.
But there have also been calls for an overhaul of the system for dealing with complaints against MPs, which gives responsibility for investigating alleged lapses to independent commissioner Kathryn Hudson, but allows the Commons Standards Committee - made up of 10 MPs and three non-voting lay members - the final say on adjucation and setting a penalty.
The committee last week overruled Ms Hudson's recommendation that Mrs Miller should repay £45,000 of expenses claimed on a house shared with her parents, and instead told her to hand back £5,800 and say sorry for failing to co-operate fully with the 14-month inquiry.
But Mrs Miller was accused by a Labour backbencher of bullying the watchdog, after it was revealed she told Ms Hudson it would be "irrational, perverse and unreasonable" to uphold the complaint against her and warned that she might go over the commissioner's head to ask the Standards Committee to intervene.
The chairman of the Independent Parliamentary Standards Authority, Sir Ian Kennedy, said it was time for MPs to give up the power to judge themselves, just as they gave up powers to police their own expenses following the 2009 scandal.
"MPs marking their own homework always ends in scandal. It happened with expenses. It will happen with standards investigations too," Sir Ian told the Sunday Times. "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."
Conservative chairman Grant Shapps agreed that the system should be reviewed, but said it did not necessarily need reform.
He told Sky News: "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."
But Labour accused Prime Minister David Cameron of "failing to act" and promised reform if it wins next year's general election.
"We need a system which commands public confidence, and what we have at the moment clearly doesn't do that," said shadow leader of the Commons Angela Eagle.
"We need reform so that people have faith that MPs are properly held to account. David Cameron has failed to act but Labour won't let this failing system go unreformed."
Former Tatton MP and anti-sleaze campaigner Martin Bell told BBC1's Sunday Politics programme: "I don't think there should be a Committee on Standards. I think the commissioner should make a report and there has to be justice for the MP complained against, then the committee of the whole House can consider it."
Mr Bell said Mrs Miller's case was yet further proof that the House of Commons is "incapable of regulating itself".
Mr Shapps said the Culture Secretary should be allowed to "get on with her job" after she apologised "unreservedly" to the Commons last Thursday as required by the Standards Committee.
But her 32-second apology was judged inadequate by almost three-quarters of voters (73%) who took part in a poll for the Mail on Sunday, while similar numbers (75%) felt Mr Cameron was wrong to offer her his support.
Some 78% of those questioned by Survation said she should forfeit her Cabinet post, 66% said she should lose powers over press regulation a nd 68% said she should be sacked as MP for Basingstoke. Ominously for Mrs Miller, 82% of those identifying themselves as Tory supporters thought she should be removed as Culture Secretary.
And Lord Tebbit wrote on the Daily Telegraph website: "Most Members of the Commons must have hoped that the scandals over fiddled expenses had at least calmed down, even if not gone away. Now Mrs Miller has not just re-ignited the flames but, by the arrogance of her response to the scandal, poured petrol on the fire."
Ministers arguing for the need to clamp down on benefit cheats were confronted by " the spectre of Mrs Miller flaunting her twisting and bending of the rules for personal gain on a vastly greater scale and allegedly allowing her staff to threaten unpleasant consequences for those who had caught her out", said Lord Tebbit, a totemic figure on the right of the party who served for six years in the Cabinet of Margaret Thatcher.
"Having staked his authority and reputation on defending his Culture Secretary against calls for her to be fired, the Prime Minister will be damned if he now fires her and damned if he doesn't," said Lord Tebbit, who predicted the scandal would boost the UK Independence Party at next month's European elections. " The best way out of this is for Mrs Miller to resign."
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.
Work and Pensions Secretary Iain Duncan Smith suggested that she was suffering a backlash for being the minister responsible for the same-sex marriage Bill, which was deeply unpopular with many grassroots Tories.
Speaking on BBC1's Andrew Marr Show, Mr Duncan Smith said: "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, who also feel rather bitter about that."
Asked if she should rethink her position, he replied: "No, I don't think so."
And he warned: "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."
:: Survation interviewed 1,001 voters on April 4 for the Mail on Sunday.
A member of the Standards Committee said he was in favour of "improvements" to the current system but cautioned against taking the final say on penalties for misbehaviour away from MPs.
Conservative MP Geoffrey Cox warned that handing the right to sanction MPs to an external regulator could raise constitutional issues, as the watchdog could have the power to change the shape of a government - particularly in times of a narrow majority - by handing down a lengthy suspension or even expulsion from the Commons.
Mr Cox told BBC Radio 4's Westminster Hour: "I think the problem is a constitutional one.
"Anybody who has the power to expel a Member of Parliament from the House of Commons has an enormous power to alter governments, to change the shape of political history.
"I think what the critics of the current system have to answer is if external regulation is going to be introduced, who is to do it, and to whom is that person or regulator to be accountable?"
While MPs are accountable to the electorate through the ballot box, in the case of an independent regulator "t he only conceivable possibility would be to hand it to a court", said Mr Cox.
"That would involve real problems, constitutional problems, of the separation of powers. I'm not at all sure the judiciary would want to have the powers," he said.
And the Torridge & West Devon MP added: " Nowhere in the world - certainly in no major democracy - has there been complete external regulation."
Mr Cox said he was " all in favour of improvements to the current system" and indicated he was willing to consider allowing a vote to the three non-politicians on the 13-member committee.
He declined to say what he thought should happen to Mrs Miller: "The consequences of what we found must be for others, but what cannot be said is that the committee was in any way deliberately or insincerely seeking to rescue the member from the consequences of her actions. That is for others to judge."