The Independent "anti-sleaze" MP, Mr Martin Bell, had a legal bill secretly paid for him during the general election campaign by Labour and the Liberal Democrats, it was alleged last night.
The £9,400 payment was not declared on his election expenses return, the Daily Mirror claimed.
The paper said the veteran BBC war correspondent could now be prosecuted and fined up to £5,000 if found guilty of breaking polling laws, and his election could be declared void.
Mr Bell was said to have first insisted, when asked by the paper about the payment, that legal advice, paid for by Labour and the Liberal Democrats, was given free, and then to have said there was no need to register it.
He told the paper: "It doesn't particularly worry me. I have done nothing wrong."
Labour and the Liberal Democrats stood down their candidates to let Mr Bell challenge the Tory former minister, Mr Neil Hamilton - the man at the centre of the cash-for-questions affair - in the Cheshire seat of Tatton.
Last night, a Labour spokesman said the money had been paid but would not confirm the amount. He told PA News: "Labour and the Liberal Democrats provided Martin Bell with financial assistance to ensure he had the legal advice he needed at a critical moment. You have to pay for legal advice."
The advice is understood to have been required by Mr Bell because Mr Hamilton was threatening legal action against him.
Mr Bell told The Mirror he had not known the advice was being paid for. "I thought it was grace and favour advice. I don't mind that it was paid for.
"This is not a campaign expense because it was not spent promoting the candidate. No one is more careful and scrupulous about declaring money received."
The paper said Mr Bell was advised by City lawyer Piers Coleman when Mr Hamilton threatened legal action over Mr Bell's plan to stand as an "Anti-Corruption" candidate.
In the end, Mr Bell was advised to stand as an Independent because Mr Hamilton had not been found guilty of any offence.