BBC2's Newsnight revealed that Sally Hammond - who became a part-time secretary to Mrs Spelman in 1999 - was "shocked" to discover just how much she was paying to nanny Tina Haynes.

Ms Haynes was employed by Mrs Spelman when she became an MP in 1997 to look after her children and do secretarial work.

However, according to Newsnight, Mrs Hammond found that Ms Haynes did little or no secretarial work to justify the payments.

Mrs Hammond - the wife of Tory front bencher Stephen Hammond - was said to have become aware of the situation because she could not understand why Mrs Spelman had so little money available for office expenditure.

She took her concerns to shadow cabinet member Peter Ainsworth - who she had worked for in the past - who in turn took it up with Chief Whip James Arbuthnot and the arrangement was stopped.

However Newsnight said that a number of Tory MPs who are familiar with Mrs Hammond's version of events have now contacted the chairman of the backbench 1922 Committee, Sir Michael Spicer, demanding she should be sacked.

A party spokesman said that Mrs Spelman was co-operating fully with the inquiry into the matter by the Parliamentary Standards Commissioner John Lyon.

"Caroline Spelman asked for the inquiry herself and will happily provide all relevant information to the parliamentary commissioner," the spokesman said.