The nanny employed with taxpayers’ cash as a constituency secretary by the Tory party chairman, Caroline Spelman, is understood not to have written letters or to have resolved constituents' queries.

Spelman is to go before Parliament's standards commissioner John Lyon tomorrow to explain exactly what secretarial duties her nanny performed and why she received parliamentary expenses.

Although she claims she acted within the rules, David Cameron, the leader of the Conservative party yesterday personally ordered her to report to Lyon.

Spelman, who as chairman is responsible for ensuring Tory MPs do not break the rules on expenses, has insisted that she paid Tina Haynes from 1997 to 1998 to act as her constituency secretary between 9am and 3pm every day.

But although she worked five days a week, Haynes is not believed to have fulfilled the key role performed by most MPs' constituency secretaries: answering letters and dealing with their queries.

Instead, according to Conservative sources, she was responsible for answering Spelman's home phone, which the MP listed as her constituency office number, for filing and dropping documents in the post.

Yesterday Haynes said her job included both childcare and duties such as posting letters, dealing with telephone calls and faxing or e-mailing documents for Spelman during a period in 1997-8 when the MP was using her home address as her constituency office.

Spelman insists that paying Haynes from her staffing allowance was legitimate because she was working as a secretary during school hours and providing childcare later in the day.

Haynes has agreed her main role was as Spelman’s nanny, a job she did for 5½ years.

Spelman did not pay Haynes cash for nannying but provided free room and board.

Spelman said yesterday: “At the time I thought it was entirely within the rules and that is still my belief.”

Labour MPs have said that they will call for an investigation if Lyon does not.

Spelman, the MP for Meriden, said hiring her nanny as her secretary was “a practical solution as she could deal with the secretarial side while the children were at school and then after school provide childcare for my kids . . . the chief whip then made me aware that such an arrangement could be open to misinterpretation”.

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