Conservative Party chairman Caroline Spelman is to be investigated over public money she paid to her nanny, Parliament's standards watchdog announced on Tuesday.
John Lyon, the Parliamentary Commissioner for Standards, will probe payments made from Spelman's parliamentary staffing allowance to Tina Haynes for secretarial work, a spokeswoman for his office said.
Haynes received the money as well as free board and lodging in return for childcare. Spelman said she thought she had acted within the rules.
In a statement, Lyon's office said the inquiry was launched after talks with parliament's Committee on Standards and Privileges, the public body which oversees his work.
"Having carefully considered the matter the commissioner has recommended to the committee that exceptionally he should conduct an inquiry," the statement said. "The committee has accepted that recommendation."
Spelman said Haynes helped her deal with a backlog of correspondence left after the death of her constituency's previous MP Iain Mills six weeks before the 1997 general election.
The arrangement, which began when Spelman was elected as an MP in 1997, ended after she hired a separate secretary following advice from the party's chief whip.
The matter is the latest expenses row to hit Conservative leader David Cameron, who expelled MP Derek Conway from the party in January for abusing staff allowances by paying his son for work he appeared never to have done.
Earlier this month, two Conservative MEPs stood down from their party positions in the European parliament over their payment of thousands of pounds of expenses to family companies.
The staffing allowance is intended to meet the cost of assistants helping MPs with their parliamentary work, and is not meant to cover expenses incurred running their private lives.
