Ms Spelman met John Lyon, the Parliamentary Commissioner for Standards, to ask him to look into allegations that she misused funds.

In a statement, his office said it would be "exceptional" for him to investigate a matter from more than seven years ago. The case in question dates from 1997.

Ms Spelman insists she did nothing wrong in employing her nanny, Tina Haynes, as a secretary for a number of months after being elected to the Commons in 1997.

The Tory MP says the nanny was doing administrative work at her home - which she was using as her constituency office - as well as providing childcare services outside school hours.

But Labour MP John Mann has called on her to pay back the money claimed from her parliamentary allowances unless she could produce proof of the secretarial services Ms Haynes provided.

The row comes amid intense scrutiny of MPs' expenses and a series of controversies over the last week involving Conservative MEPs' use of their Brussels allowances.

One Tory MEP insisted he had done nothing wrong in claiming £2,000 towards a trip to the US during which he attended his son's wedding.

David Cameron warned MPs and MEPs that they must only claim expenses that "reasonable" people would agree with. The Tory leader said it was no longer enough to argue that claims were within the rules.

Mr Cameron said there was a need for "quite a big cultural change" in parliamentarians' attitude to their expenses regimes.