In a surprise development, Vanessa Gearson, who is deputy director of the Tory party and was employed in the leader’s office until two months ago, explained why she had taken independent legal advice over her part in the affair.

She claimed that she was unhappy with attempts by the leadership to make her sign a statement corroborating Mr Duncan Smith’s version of events.

A spokesman for Ms Gearson made a statement to The Times yesterday staunchly defending her decision to voice concerns over the way the Tory leader paid his wife Betsy out of public funds to be his diary secretary.

Ms Gearson had been forced to speak out to protect her integrity and had no axe to grind against Mr Duncan Smith, the spokesman claimed.

According to yesterday’s Sunday Telegraph, Ms Gearson sent an internal e-mail on January 30 this year in which she stated her concerns about payments to Mrs Duncan Smith.

The Parliamentary Commissioner for Standards, Sir Philip Mawer, has now been sent a dossier containing the e-mail and other central allegations by the Newsnight reporter Michael Crick.

Sir Philip must now decide whether or not the Tory leader broke parliamentary rules in the way he paid his wife.

Mr Duncan Smith strenuously denies any impropriety and has issued a lengthy statement through his lawyers explaining his wife’s duties. He said he was himself referring the matter to Sir Philip in an attempt to clear his name.

“I completely and absolutely rebut any allegation about wrong-doing,” he said in a statement.

“These allegations are without foundation and are malicious and I will be contacting the Commissioner first thing on Monday morning.

“I have also instructed my lawyers to review the press reports with a view to taking legal action.” The suspicion among IDS loyalists is that those pushing the rumours are in some way connected with or being used by protagonists in a plot to oust him as leader.

Ms Gearson has been told she faces the prospect of disciplinary action and has been summoned to a meeting with the Tory chairman, Theresa May, today.

Friends of Ms Gearson point out that as deputy director of Central Office and a future Tory candidate she is not someone with an agenda to undermine Mr Duncan Smith.

A spokesman for Ms Gearson said she stood by her central allegation: “She does not feel that Betsy did enough work to justify the salary she was paid.

“Vanessa feels she is doing the right thing and she has other people who will say she is a decent honourable person.

“She does not want to cause trouble for the party or for Iain. She simply feels she was asked to sign something in a statement she did not feel she could agree with.

“If there is a reasonable explanation she would be delighted but as it stands she does not see how there can be one.” She was acting “more in sorrow than in anger”, the spokesman said.

He alleged that pressure had been applied to try to force her to sign a statement bearing out Mr Duncan Smith’s version of his wife’s employment. She claimed she felt so pressured to defend Mr Duncan Smith that she took independent legal advice.

Mr Duncan Smith said: "These allegations are without foundation and are malicious. I will be contacting the commissioner first thing Monday morning. I have also instructed my lawyers to review the press reports with the view to taking legal action."

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