"During the period of 1997 to 1998, I had two roles, one helping Mrs Spelman with childcare and another providing secretarial help to her as a MP," she said.
"My roles and responsibilities were general administration which entailed tasks such as posting of letters, answering phone calls at the home address, (and) faxing or posting documents to Mrs Spelman whilst she was in London.
"This was performed during the hours that her children were at school. On Fridays any help with directions to constituency events was given."
BBC correspondent Gary O'Donoghue said the statement went some considerable way to support Mrs Spelman's account of events.
But Ms Haynes does not specifically say she was employed as the constituency secretary, or that this role amounted to 30 hours a week.
Ms Spelman, MP for Meriden, earlier said that she believed she had acted "entirely within the rules", but would nonetheless refer the matter to the parliamentary standards commissioner.
Speaking outside her home in Solihull, Ms Spelman, who recently took charge of improving the Conservatives' record on expenses, said that when she became MP in 1997, following the untimely death of her predecessor, her home became the constituency office.
My prime concern was to make sure my constituents' needs were rapidly attended to
She said that using her nanny to do constituency administration - answering the phone and dealing with post - during school hours was a "practical solution".
Once the children came home from school, she said Ms Haynes took on a nannying role for which she received board, lodging and use of a car at the MP's personal expense.
"As a working mother that offered a practical solution because she could deal with the secretarial side when the children were at school," Ms Spelman said.
"My prime concern was to make sure my constituents' needs were rapidly attended to as a new MP."
The arrangement came to an end when the Conservative Party's chief whip told Ms Spelman it could be "open to misinterpretation", and she appointed a separate constituency secretary.
Shadow Chancellor George Osborne earlier defended Ms Spelman, saying she was "someone of enormous integrity and honesty" and she was the "last person in Parliament" who would do something wrong.
The allegations have come at a sensitive time for both the Conservatives and Ms Spelman, who played a role in prompting the resignation on Thursday of Tory MEP leader in Brussels, Giles Chichester.
Mr Chichester stepped down as leader after Ms Spelman asked him to answer allegations that he had broken European Parliament rules on expenses.
Newsnight interview Caroline Spelman's former nanny
And on Friday another Tory MEP, Den Dover, was replaced as the party's chief whip in Brussels.
Mr Dover denies breaking any rules in paying his wife and daughter a reported £750,000 for work over nine years, and the Conservatives said the move was unrelated to the issue of expense.
Former standards commissioner Sir Alistair Graham said the "constant stream of stories" about MPs' expenses was "very damaging" to the parliamentary system.
"It's not a party political matter - it is a matter of finding acceptable systems which will satisfy the public that members of parliament are not taking advantage of very generous rules which are loosely monitored," he told the BBC.
Labour MP Kevan Jones said there was "a big question mark" over Ms Spelman's use of allowances.
"Clearly, old habits die hard in the Tory Party despite what their leader says," he said.
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