Media playback is unsupported on your device Media caption Iain Duncan Smith: "I'm supportive of Maria, because I feel if we're not careful we end up in a witch-hunt"

MPs should do "whatever it takes" to stop rows over their expenses "eating away at the credibility of Parliament", a cabinet minister has said.

Iain Duncan Smith was speaking after the independent parliamentary watchdog said MPs should "no longer mark their own homework" on ethics.

It comes after a committee of MPs overruled investigators probing Culture Secretary Maria Miller's expenses.

Former Conservative chairman Lord Tebbit has called on her to resign.

Asked whether Mrs Miller had his full support, current Conservative Party chairman Grant Shapps said it was not a matter for him and he was "satisfied" that she had complied with Parliament's wishes.

The row over the culture secretary's expenses dates back to December 2012 when the Daily Telegraph reported she had claimed £90,718 in expenses towards mortgage payments on a house in south London that the MP shared with her parents.

Who does what on MPs' expenses and standards The Independent Parliamentary Standards Authority sets MPs' pay, pensions and expenses and authorises claims

The Parliamentary Commissioner for Standards investigates complaints against MPs and recommends action

The Commons Standards Committee decides sanctions to be taken against MPs What is the row about? Profile: Maria Miller

The parliamentary commissioner for standards, who conducted an investigation into the culture secretary's expenses, ruled she should repay £45,800 but the House of Commons Committee on Standards, which has the final say on issues on ethics and disciplinary matters, cut this to £5,800.

The 13-strong committee is mostly made up of MPs and its three independent members are not allowed to vote.

'Reasonable and honest'

Mr Duncan Smith, who is work and pensions secretary, told the BBC's Andrew Marr Show that MPs' expenses and the wider issue of standards was corrosive.

Asked whether he backed an independent system, he said: "I am very happy for that to be debated. I am among a number of those who feels this goes on and on eating away at the credibility of Parliament.

"Whatever it takes to restore the credibility of Parliament is right. I am very open to independent people looking at this. Personally the sooner we can get rid of this nonsense the better."

Image caption Maria Miller apologised to MPs for her attitude towards an inquiry into her expenses

Mr Duncan Smith said he believed that Mrs Miller was an "reasonable and honest" person and had apologised.

He said there was a "lot of antipathy" towards Mrs Miller because of her role in drawing up tougher regulation of the press in the wake of the phone hacking scandal and the Leveson Inquiry recommendations.

Asked whether she should stay in the cabinet, he said it was a "matter that the prime minister has to take consideration of and she herself".

"I am supportive of Maria because if we are not careful, we can end up in a witch-hunt of somebody".

However, writing in a blog for the Daily Telegraph, Lord Tebbit accused Mrs Miller of "arrogance" in her response to the affair.

He is the most senior Conservative to call for the culture secretary to resign, saying the row had undermined the government's message that "we're all in it together".

He added that the prime minister, having "staked his authority and reputation" on defending Mrs Miller, would be "damned if he now fires her and damned if he doesn't".

"The best way out of this is for Mrs Miller to resign," he said.

'Progress'

The authorisation of MPs' expenses was transferred to an outside body after a public outcry in 2009 about revelations of inappropriate claims made in the past.

However, complaints about MPs conduct - including allegations they have abused the expenses system - are investigated by the parliamentary commissioner, who is overseen by the Committee for Standards.

We need a system which commands public confidence, and what we have at the moment clearly doesn't do that Angela Eagle, Labour

Speaking to the Sunday Times, Sir Ian Kennedy - chairman of the Independent Parliamentary Standards Authority - said an end to the current system of self-regulation of standards was now "the only way forward".

MPs "marking their own homework always ends in scandal", he said.

Mrs Miller's mortgage claims, which relate to the period between 2005 and 2009, "couldn't happen under Ipsa", he said, adding that "great progress" had been made under the new regime.

But he went on: "There is a lesson from Ipsa which ought to be learnt with the commissioner for standards too.

"She should be given the freedom to carry out her work and not have her wings clipped by MPs.

"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."

'Irrational'

Former independent MP Martin Bell said he believed the Commons standards committee should be abolished.

"I think the commissioner should make a report and there has to be justice for the MP complained against, then... the whole House can consider it," he told the BBC's Sunday Politics.

And Labour's Angela Eagle also backed changes to the remit of the committee.

"We need a system which commands public confidence, and what we have at the moment clearly doesn't do that," the shadow leader of the House of Commons said.

In addition to ordering the culture secretary to repay £5,800, the committee said Mrs Miller's submission of "incomplete" evidence to the inquiry had breached the MPs' code of conduct and said she should apologise to MPs "for her attitude to the commissioner's inquiries".

Emails released by the committee revealed Mrs Miller told the commissioner investigating her that she might go over her head to ask MPs to intervene.

A number of newspapers have called for her resignation.

A poll carried out by Survation for the Mail on Sunday suggested 78% of the public think that Mrs Miller should resign as a cabinet minister.

The survey was conducted online on Friday among 1,001 people.