The party leader, his wife and the claims that won't go away

Party official expressed qualms over work of Betsy Duncan Smith - but new poll shows a dramatic gain for party

In a party that does precious little to encourage women to become politicians in their own right, Tory wives have for decades acted as a kind of invisible backbone.

Many turn out, unpaid, to support their MP husbands at public functions. Others do more than that, organising their husband's affairs and acting as a channel between the MP and the voters he represents. Paying them is a legitimate use of an MP's parliamentary allowance, if they are genuinely doing constituency work. But an arrangement that would be considered normal for a backbench MP or shadow minister looks odd when it is continued by a party leader on a salary of £121,000 a year, who can call on party staff to run his affairs.

At Conservative Central Office, the issue of how a Tory MP manages his parliamentary allowances became more sensitive last year after Michael Trend, the MP for Windsor, was exposed as a cheat, bringing his political career to a quick end.

The "recent difficulties experienced by Michael Trend" were much on the mind of Vanessa Gearson, head of Mr Duncan Smith's office when she sent her now famous email to Theresa May, the party chairman, last January. "As you know BDS (Betsy Duncan Smith) has only just ceased to claim £18,000 off his Parliamentary Office Costs Allowance and the last thing we would wish is for a Crick-style investigation of his financial arrangements," she said.

But a "Crick-style investigation" is exactly what they got, after the indefatigable Michael Crick, an investigative journalist, had been tipped off in May about the rumblings inside Central Office. According to The Sunday Telegraph, Mr Crick scoured Chingford, interviewing party officials, Tory councillors and 18 local organisations to establish how much constituency work Mrs Duncan Smith was doing for her money.

After several weeks' investigation, Mr Crick was ready to go on BBC's Newsnight to allege that the answer was very little. Newsnight's editors were reported to be delighted with the story and planned to put it out on 2 October, just ahead of the Conservatives' annual conference. But after the barrage of criticism that the BBC had endured during the Hutton inquiry, over allegations broadcast by their staff journalist Andrew Gilligan, the corporation's senior management insisted on caution. Mr Duncan Smith was given three days' notice of the intended broadcast, during which Conservative Party lawyers prepared a detailed argument that Betsy Duncan Smith had earned her money by working more than 25 hours a week during a transition period while Mr Duncan Smith's office was being reorganised.

After hearing from the lawyers, the BBC's management prevented Mr Crick's report from being broadcast. Mr Duncan Smith has said he will sue anyone who repeats Mr Crick's allegations.

But it is one of those stories that refuses to go away. Mr Crick, writing in The Sunday Telegraph, has defended his decision to submit the evidence to the Parliamentary Commissioner, Sir Philip Mawer. He wrote: "IDS can hardly criticise me for going to Sir Philip.

"Ten days ago, his lawyers suggested that the BBC should pursue these allegations through the traditional parliamentary mechanism, by which I assume they meant the Standards Commissioners.

"I believe that Sir Philip is the only man who can get to the bottom of this matter. It is in the interests of good government and, if the claims turn out to be unfounded, it should also be in the interests of Iain Duncan Smith."

The Tory leader's problems are compounded by a rift with Ms Gearson, who is now deputy director of Conservative Central Office and the party's candidate in Cheltenham. According to The Sunday Times, she resisted pressure from Mr Duncan Smith to issue a public statement supporting his claim that he had done nothing wrong.

A Conservative Party spokesman said last night: "We reject Miss Gearson's claims as reported in The Sunday Times that she was subjected to pressure to make a false statement in relation to this matter. Once the facts were made clear to her last January, she sent an email making clear that her concerns had been addressed. At no time has she been subjected to pressure to make false statements."