Maria Miller row is at risk of becoming witch-hunt, says Iain Duncan Smith

Maria Miller is the victim of 'media antipathy' over her role introducing Leveson proposals, said Iain Duncan Smith. Photograph: David Jones/PA

Iain Duncan Smith has offered tentative support for a proposal to end the right of MPs to regulate their own affairs, warning that the continuing focus on expenses because of the row over Maria Miller's housing claims is "eating away at the credibility of parliament".

As a poll found that 82% of Tories believed that Miller should lose her jobover her expenses, the work and pensions secretary said he was "very open" to a proposal by parliament's expenses watchdog to introduce independent regulation of MPs.

"I think the sooner we can get rid of this nonsense the better," he said. But Duncan Smith offered strong personal support for the culture secretary as he came close to suggesting that she has been the victim of a witch-hunt.

Speaking on the Andrew Marr Show on BBC1, he said Miller was a victim of "media antipathy" in light of her role introducing the Leveson proposals. Many Tories were also angry with her after she introduced gay marriage, he added.

The work and pensions secretary raised the prospect of a major overhaul of the way MPs regulate their affairs as Miller faced a third consecutive day of damaging headlines about her expenses.

The culture secretary was forced by the Commons standards committee to repay £5,800 in overclaimed expenses in mortgage payments related to her "second" home in Wimbledon. She was also asked to apologise for her conduct towards Kathryn Hudson, the parliament standards commissioner, after documents showed that she accused the watchdog of acting outside the law.

Duncan Smith, who worked closely with Miller in her previous ministerial post as minister for the disabled, offered strong personal support for the culture secretary. He said: "I am enormously fond of her. She has done a very good job in a very difficult set of circumstances with the Leveson inquiry that has stirred up a lot of media antipathy to her.

"And also the gay marriage stuff – there are a lot of Conservatives out there who, perhaps, were not necessarily in support of it all and so feel rather bitter about that. I have known her to be a reasonable and honest person."

Duncan Smith said the prime minister would have to consider the row over Miller's expenses. But he said: "I am supportive of Maria because if we are not careful we end up with a witch-hunt of somebody. The committee has told her to repay some money and she should apologise and she has done both those."

In a sign that the government acknowledges the damage from another row over expenses, Duncan Smith said he was open to a proposal by Sir Ian Kennedy, the chairman of the Independent Parliamentary Standards Authority (Ipsa), to end the right of MPs to sit in judgment on their peers.

John Mann, the Labour MP who lodged the original complaint about Miller, has been highly critical after the standards committee, which includes 10 MPs and three non-voting lay members, recommended that Miller should repay £5,800 in expenses. This was considerably lower than the £45,000 proposed by Hudson.

Duncan Smith said it may be right to end the way in which MPs have the sole right – apart from the non-voting lay members of the standards committee – to sit in judgment on the findings by the independent standards watchdog.

He said of the proposals by the Ipsa head: "I am very happy for that to be debated. I am amongst a number of those who feel this goes on and on and on eating away at the credibility of parliament. Whatever it takes to restore that credibility – I am very open to independent people looking at this. Personally I think the sooner we can get rid of this nonsense the better."

A poll by Survation for the Mail on Sunday found overwhelming opposition to Miller. The poll found that 78% thought Miller should lose her cabinet post. It found that 82% of Tories thought she should go.

An unnamed minister told the Sunday Telegraph that Miller should lose her cabinet post because her conduct was "incompatible" with her role as a cabinet minister.

Kennedy, the Ipsa head, said Miller's conduct showed the need to end the right of MPs to regulate their own affairs. Ipsa was established after the expenses scandal in 2009 when MPs handed the running of expenses to an independent body. Wrongdoing is investigated by the standards commissioner but the standards committee makes the final judgment on any findings.

Kennedy 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."