Conservative leader says he wants people with no background in Tory politics to consider standing as candidates for parliament

David Cameron today hinted at a desire to clear out the Conservative old guard when he said he wanted people with no background in Tory politics to consider standing for parliament as Conservative MPs.

In a move that suggests he feels the modernisation of the Conservative party has not gone far enough, Cameron said he would change party procedures to allow new people to put their names forward.

His comments are significant because the Tories will have to find candidates to stand in safe seats where MPs are standing down as a result of the expenses scandal.

Four backbenchers have already said they will not seek re-election as a result of the revelations, and more are expected to follow.

In an interview on BBC1's Andrew Marr programme today, Cameron said he did not want parliament to be full of "robots".

"What I'm going to do today is I'm going to reopen the Conservative candidate list to anybody who wants to apply," he said.

"They may not have had anything to do with the party before.

"But I'm saying, if you believe in public service, if you share our values, if you want to help us clean up politics, come and be a Conservative candidate."

The development suggests he would like to use the expenses controversy as an opportunity for a clearout of some of his party's MPs.

He has been concerned that recent stories about the lifestyles of Tory MPs have reinforced perceptions that his party is out of touch with ordinary voters, and he knows some of his older MPs have little enthusiasm for his modernising policies.

Cameron also said he wanted his party to use more "open primaries" – selection contests open to people who are not party members – to select Tory candidates and that, if he were prime minister, he would allow more free votes in parliament if bills were not part of his party's manifesto.

He added that the decision of his former aide, Andrew Mackay, to announce that he would stand down from parliament was the correct one.

The Tory leader said he had had a "straightforward conversation" with Mackay about it yesterday before the announcement was made.

"It was absolutely the right thing for him to retire," he said.

"It was one of the most serious cases. It was a misjudgement and he is paying the price for that."

Mackay's departure, marking Cameron's first loss from his inner circle, came after two weeks in which Labour had appeared more damaged than the Conservatives by the stream of revelations in the Telegraph.

His expenses claims came to light as a result of checks by Tory officials ahead of publication in the Telegraph.

Paperwork showed that while he claimed the London home for which both he and his wife, Julie Kirkbride, the Tory MP for Bromsgrove, were named on the mortgage, as his second home, he did not appear to have a main home of his own since he did not have a house in his Bracknell constituency.

MPs with only one home are not entitled to a second home allowance.

The spotlight will now inevitably turn on Kirkbride, who came under further pressure today after the News of the World reported that her brother, Ian, had lived at the couple's Worcestershire home since 2004.

She rushed out a statement saying her brother spent time at both of their homes, but insisted she had nothing to apologise for.

"My brother Ian stays in my Bromsgrove apartment and in my London home from time to time to help look after my son," she said.

"I claim no expenses for my brother and neither do I pay him or claim for his help. He also acts as a volunteer in helping me with office work and administration."

Claims that he had been living there "rent-free" at taxpayers' expense were a "total distortion," she said.

Yesterday, shoppers queued in Bromsgrove town centre to sign a petition calling for her to resign, but the Tory leader said: "She genuinely lives in London, her children go to school in London. We have to look at that case separately."

Cameron said the party had already used open primaries to select candidates in some constituencies, and they had been very successful.

"It worked fantastically well and I want to see more of it," he added.

He suggested that the use of primaries could lead to celebrities such as such as Joanna Lumley becoming MPs.

The three main parties fear they could be severely punished as voters desert to smaller parties untainted by the expenses scandal.

With dozens of MPs across all parties now said to be considering stepping down, the former cabinet minister Ian McCartney announced he would quit at the next election.

Colleagues said although he was not regarded as having been a particularly excessive claimant, he had suffered a furious backlash from constituents in Makerfield over his published expenses.

He had already offered to pay back around £15,000 after purchasing items including champagne flutes. McCartney was for many years regarded as an invaluable and trusted bridge between Tony Blair and Gordon Brown.

The Sunday Telegraph has placed senior Liberal Democrat MP Malcolm Bruce in the spotlight, saying he claimed for thousands of pounds towards the running of both his London flat and his constituency home, where his wife worked for him.

Normally MPs can only claim expenses for their second homes.

The newspaper said he was one of 200 MPs who had been able to claim money for a main home, in addition to their second home, because their spouses worked there on parliamentary business.

It said Derek Conway, the MP expelled last year from the Tory party over payments to his two sons, was able to claim for office expenses at a family home in Morpeth, Northumberland, as well as mortgage interest on his designated second home in London, although the Morpeth house is more than 300 miles from his Old Bexley and Sidcup constituency.

The Labour minister Quentin Davies is said to have claimed more than £10,000 to repair window frames at an 18th-century mansion in Lincolnshire designated as his second home.