Mrs Spelman insists she acted within the rules over expenses
Conservative chairman Caroline Spelman is to be investigated by Parliament's standards watchdog over her use of expenses to pay her nanny.
Standards Commissioner, John Lyon, had previously said it would be exceptional to carry out an inquiry into matters dating back more than seven years.
Mrs Spelman, MP for Meriden, says her nanny, who she employed in 1997 and 1998, was paid for secretarial work.
MPs' allowances are only for activities directly related to their jobs.
Conservative Central Office has said that Tina Haynes - who was Mrs Spelman's nanny from 1997 to 2002 - also worked as her constituency secretary for six hours a day between 1997 and 1998. Later it emerged she had been paid until March 1999.
Mrs Spelman said Ms Haynes did administrative work at her home, used as her constituency office, as well as providing childcare services outside school hours.
The arrangement ended when the Conservative Party's Chief Whip told Mrs Spelman it could be "open to misinterpretation", and she appointed a separate constituency secretary. The party says it was not thought any rules had been broken.
As somebody who has worked with Caroline for a long time, I've not the slightest doubt that her name will be cleared
Eric Pickles Conservatives
Mrs Spelman, who recently took charge of improving the Conservatives' record on expenses, has said that she believed she had acted "entirely within the rules".
But she held a meeting with Mr Lyon on 9 June and asked him to investigate in order to clear her name.
On Tuesday Mr Lyon's office said in a statement that he had "considered carefully" her request "despite having received no formal complaint about her conduct and that the events complained of were more than seven years ago".
Mr Lyon had recommended that "exceptionally" he should begin an inquiry into whether Mrs Spelman had broken Commons rules "in force at the time" - and the standards and privileges committee had accepted his recommendation.
For part of the period, it is claimed Ms Haynes was working at Mrs Spelman's home in Kent - 140 miles from her West Midlands constituency.
Mrs Spelman has said she had to use her home as a constituency office because of administrative problems after the sudden death of her predecessor as Meridan MP.
Newsnight's investigation into Caroline Spelman's expenses
Labour MP John Mann said Mrs Spelman should pay the money back and said it was "rather unusual" to employ a secretary 140 miles from the constituency.
"This is taxpayers' money we're talking about, there's lots of hard working families across the country who would love to get a nanny paid for by the taxpayer, but they're not getting it and neither should Caroline Spelman."
But for the Conservatives, Eric Pickles said the fact Mrs Spelman had referred the matter to John Lyon's office herself showed her "integrity".
"She wants an opportunity to clear her name and as somebody who has worked with Caroline for a long time, I've not the slightest doubt that her name will be cleared," he told the BBC.
An MPs' committee headed up by Speaker Michael Martin is reviewing the whole expenses system - in the wake of the case of Derek Conway, a Conservative MP who was reprimanded for the amount he had paid his son to work as a Parliamentary researcher.
The story about Mrs Spelman's expenses also followed the resignation of the Conservative MEP leader in Brussels, Giles Chichester over allegations he had broken European Parliamentary rules on expenses.
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