Tory leader David Cameron will be hoping that the sting has been drawn from the Spelman affair by a statement from nanny Tina Haynes, who said that her work for Mrs Spelman in 1997/98 included both childcare and administrative duties.

But Labour MP John Mann insisted that if Ms Haynes was indeed employed as a secretary, she would have left a "paper trail" of computer files and initialled documents, and said Mrs Spelman should produce them or pay back the funds she claimed from her parliamentary staffing allowance.

Mrs Spelman is due to meet Parliamentary Standards Commissioner John Lyon on Monday after she decided on Saturday to refer the case to the watchdog herself so that he can judge whether rules were broken.

She insists she did nothing wrong, and has won the backing of shadow chancellor George Osborne, who described her as "someone of enormous integrity and honesty".

Meanwhile, there were fresh questions over Tory expenses claims at the European Parliament, as the Sunday Times newspaper reported that Conservative MEP Sir Robert Atkins attended his son's wedding in the USA during a visit paid for from parliamentary allowances.

Sir Robert could not be reached for comment on Saturday night, but he told the Sunday Times that the wedding coincided with an invitation from the Republican National Committee to make a visit to meet party members in New York, New Jersey and Connecticut.

The report follows the resignation of the Conservative leader in the European Parliament Giles Chichester after it emerged he transferred more than £400,000 of staff expenses to a private family company.

The party's chief whip in Brussels, Den Dover, was also replaced after insisting there was nothing amiss in paying his wife and daughter a reported £758,000 over nine years through a company for secretarial and support services.

The string of revelations about expenses claims is an embarrassment for Mr Cameron, particularly as he had given both Mrs Spelman and Mr Chichester roles in overseeing the propriety of the use of public funds by MPs and MEPs.