A lifelong Conservative voter voiced bewilderment and anger yesterday when she was unmasked as the fourth intermediary used by David Abrahams to channel secret donations to Labour.

Janet Dunn, a secretary and school lollipop lady whose husband occasionally works for the property developer, said she had no idea that a donation of £25,000 had been made in her name and could remember nothing of the transaction.

Then late last night Anthony Dunn apologised, saying that the couple had checked their accounts and Mrs Dunn had indeed done a “swap cheque” with Mr Abrahams but did not know that the money was destined for the Labour Party.

The timing of the covert gift, in January 2003, makes Mrs Dunn the first person known to have been used by Mr Abrahams for his series of proxy donations, which amounted to £600,000 over four years.

A solicitor acting for Mr Abrahams, Louis Charalambous, admitted yesterday that the property developer was behind the donation made in Mrs Dunn’s name.

Mrs Dunn, from Ponteland, near Newcastle upon Tyne, insisted that she had not written out a cheque to the party. “I knew nothing at all about it. Last night was the first I heard,” she said. Her husband, 67, said later: “We checked . . . [and] a cheque was put in and out. It was done as a swap cheque. It was just done in and out. David’s put one in and we’ve put one out.”

Mr Dunn, a land agent, said that he worked for Mr Abrahams on occasions. The couple described themselves as Tory voters. Mr Dunn said that Mr Abrahams, 63, rang him and said: “I think you better check your bank statements.”

He said: “It was David’s money and we’ve been used. We’re very upset. It’s done now, unfortunately. We can’t got backwards, unfortunately.”

The donation made in Mrs Dunn’s name was modest in comparison with some of the others.

The Labour Party said yesterday that two of the donations made in the names of a builder and secretary who worked for Mr Abrahams had been double-counted by the Electoral Commission, which reduced the total figure slightly.

Ray Ruddick gave the party a total of £172,850 and Janet Kidd gave £147,000 plus £5,000 to Harriet Harman’s successful campaign to be Labour’s deputy leader. A third man, John McCarthy, a Newcastle solicitor, made donations amounting to £257,125, higher than initially thought because his name was misspelt on the Electoral Commission website.

That Mr Abrahams was so anxious to disguise his generosity to Labour has inevitably led to speculation about his motives. Part of the remit of the inquiries into the affair announced yesterday will be to ascertain if he had something to hide.

Attention focused initially on a multimillion-pound project to turn 540 acres of Co Durham farmland into a commercial development that would potentially create 5,000 jobs in the North East. Using a technique honed over many years, the businessman was able to stay in the shadows while a two-year battle was waged to win planning consent for his scheme. Two of his proxy Labour donors, Mr Ruddick and Ms Kidd, were listed as the sole directors of the company behind the plan, Durham Green Developments, whose registered address is Mr Abrahams’s home in Gosforth.

The £25,000 cheque to cover the cost of the planning application was paid in the name of David Martin, the name that Mr Abrahams adopts for his business transactions. The application, for a site south of Durham near junction 61 of the A1(M), hit problems in late 2005 when it was blocked by the Highways Agency over fears that it would create motorway congestion.

A year later the agency changed its mind and lifted its objections. In October last year Durham City Council duly approved the plan for the first phase of the development, which involves the building of a 30-acre business park with 425,000 sq ft (39,500 sq m) of office space.

Mr Abrahams, a Labour supporter for more than 40 years, has threatened to sue anyone who implies that his covert donations to the party were made “in exchange for favours”.

Douglas Alexander, who was Transport Secretary when the Highways Agency had its surprise change of heart, insisted yesterday that he had not heard of Mr Abrahams until a few days ago. The Department for Transport said that Mr Alexander, a close ally of the Prime Minister, had not been consulted about the proposed development and “had no involvement in any part of the process”. Also in Mr Abrahams’s favour is the awkward fact, for proponents of a smoking gun theory, that Durham City Council is controlled by the Lib Dems.

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