David Cameron was under mounting pressure last night to end the political career of one of his closest allies as the MPs' expenses scandal claimed its first casualties.

Andrew MacKay resigned as Mr Cameron's senior political and parliamentary adviser after he admitted claiming a "second home" allowance when he only had one property. He received £140,952 on the London home he shares with his MP wife Julie Kirkbride, who listed it as her main home and claimed £141,779 for a house she bought in her Bromsgrove constituency. Mr MacKay, who does not have a home in his Bracknell constituency, admitted his arrangement now looked "strange" but insisted it had been approved by Commons officials. Asked if he had done anything wrong, Mr MacKay said he had made "an error of judgement that looks wrong". Tory officials say Ms Kirkbride has done nothing wrong and had also had her arrangements approved by the Fees Office. No action is planned against her.

Mr Cameron has promised to take a tough line against Tory MPs who have made suspect claims but he appears reluctant to withdraw the party whip from Mr MacKay – which would ban him from being a Tory candidate at the general election. A survey of 1,400 Tory grassroots members found that 66 per cent believe Mr MacKay should cease to be an MP. The ConservativeHome website found that 82 per cent of Tory members want MPs facing questions about their behaviour to face deselection meetings.

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On a day of shame for Parliament, Elliot Morley, a former environment minister, was suspended from the Parliamentary Labour Party after it emerged he had claimed £16,000 for a mortgage that did not exist. The police have received a complaint about his actions from the Taxpayers' Alliance. Boris Johnson, the Mayor of London and chair of the Metropolitan Police Authority, said there was a case for the police to be called in to investigate the claims made by some MPs.

Meanwhile, two Labour peers face a six-month suspension from the House of Lords after an investigation into allegations they were prepared to take "cash for amendments". A senior Labour source said Parliament was "having a collective nervous breakdown."

Today, The Daily Telegraph accuses the Justice Minister Shahid Malik, of claiming £66,827, the maximum amount allowed for a second home over three years, despite securing his main three-bedroom home in his constituency of Dewsbury, West Yorkshire, for a discounted rent of less than £100 a week. He denied breaking any rules, saying the expenses system was flawed.

The newspaper discloses that Clare Short, the former International Development Secretary who now sits as an independent candidate, claimed the full cost of her mortgage for two-and-a-half years when she was entitled only to the interest. She was asked by the Fees Office to repay more than £8,000. Last night she said she made an "honest mistake" when she switched from an interest-only to a repayment mortgage in 2003.

But the damage over the expenses saga continued to hurt Labour most, with a YouGov survey in The Sun today putting Labour on 22 per cent, its lowest-ever rating, the Tories on 41 per cent and the Lib Dems on 19 per cent.

Labour denied dithering over Mr Morley's case. Although it did not act until after the Telegraph revealed his £800-a-month mortgage claim, Labour sources say the party did not know the full details until yesterday. The party's national executive committee will consider disciplinary action against other Labour MPs when it sits next Tuesday.

Cameron aides denied he had gone soft over Mr MacKay to protect a close adviser. They said there was no need to discipline him because he had promised to abide by the verdict reached by a new Tory scrutiny panel being set up by Mr Cameron. It is likely to order Mr MacKay to repay the money.

Speaking on the BBC's Question Time last night amid a row over the expenses saga, the Lib Dem Home Affairs Spokesman Chris Huhne joined the growing number of MPs calling for the Speaker, Michael Martin, to step down after comments he made on Thursday.

Douglas Hogg, the former Agriculture minister, backed away from a confrontation with the Tory leader. On Wednesday, he cast doubt on the Tory panel's legitimacy. Last night, he agreed to repay £2,200 he claimed for maintaining his country estate "in recognition of public concern". He admitted the cost of cleaning his moat "was not positively excluded from the claim".

Greg Barker, a Tory environment spokesman, will make a "voluntary payment" for capital gains tax.