Iain Duncan Smith is facing an investigation by the Parliamentary Commissioner for Standards over his use of public funds to pay his wife, Betsy.
Michael Crick, the investigative journalist and author of a biography of Jeffrey Archer, is submitting documents and witness statements to Sir Philip Mawer after failing to persuade the BBC to let him broadcast his allegations.
Crick's decision prompted the first admission by the Conservative Party that Betsy Duncan Smith was still drawing a salary from her husband's parliamentary allowance months after he was elected leader of the Conservative Party in September 2001.
The Sunday Telegraph was told that she was paid "substantially less" than the figure of £18,000 reported in last week's Independent on Sunday, and that she earned it by working more than 25 hours a week from home.
Crick's submission is expected to include statements by party officials and from Conservatives in Chingford disputing that Mrs Duncan Smith was carrying out constituency work. Parliamentary rules permit MPs to pay their wives to help out in their constituencies but they are not allowed to use their parliamentary allowances for political purposes.
It also emerged last night that Vanessa Gearson, the Conservative Central Office official who warned that Mr Duncan Smith could face criticism over his office arrangements, has taken independent legal advice.
Ms Gearson, who headed Mr Duncan Smith's office, sent an email to Theresa May, the party chairman, in January warning that "the last thing we would wish for is a Crick style investigation into his affairs". She has since been transferred to another job in Conservative Central Office.
Mr Duncan Smith has denied any irregularity, and has threatened to sue anyone who accuses him of behaving improperly.
The allegations will add to the feverish atmosphere when Tory MPs return to the Commons on Tuesday, after a party conference dominated by rumours of plots to unseat Mr Duncan Smith. Several have already decided to sign letters calling for a vote of confidence, which could trigger a new leadership election.
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