David Cameron's local Conservative party association has admitted receiving more than £7,000 in illegal donations.
The Witney Conservative Association has voluntarily forfeited the money after it emerged the benefactors were not on the electoral roll, making them ineligible to donate to a political party.
Labour said the revelation was "shocking", coming weeks after the Conservatives capitalised fully on Labour's illegal donor scandal.
The Conservatives, who have already handed the funds to the Electoral Commission, insist the money was banked as a "genuine mistake".
It has emerged two donations received by the Witney association in August were unlawful because the givers were not registered to vote.
Roger Fletcher had donated £5,900 and Geoffrey Dobbs gave an auction prize worth £1,500.
The association handed the illicit £7,400 to the Electoral Commission on November 16th 2007.
A Conservative spokesman said today: "As soon as we became aware that these two donations were not permissible we declared and voluntarily forfeited them to the Electoral Commission."
But Labour MP John Mann, who complained to the Electoral Commission, said the donations amounted to a "shocking revelation".
Mr Mann said: "It beggars belief that David Cameron was lecturing others and questioning their integrity, when he has not even bothered to check that his own house is in order."
He continued: "In recent weeks, we have heard Mr Cameron say someone who does not know what is going on in their party is not fit to lead the country.
"Presumably he believes that is even more true for someone who does not know what is going on in their own constituency office."
Mr Cameron tried to heap personal blame on Gordon Brown for Labour's donor scandal, after it emerged the party had allowed David Abrahams to donate more than £600,000 through intermediaries.