Work and Pensions Secretary Peter Hain has admitted that he failed to register a £5,000 donation to his deputy leadership campaign by Labour's new chief fund raiser.
Mr Hain blamed an "administrative error" for the failure to inform the Electoral Commission of the donation by Jon Mendelsohn.
"In the light of recent events, it has come to my attention that a donation from Jon Mendelsohn to my deputy leadership campaign was mistakenly not registered with the Electoral Commission," Mr Hain said in a statement on Thursday night.
"Jon Mendelsohn made a personal contribution of £5,000 at the end of June 2007.
"We wish to make clear that this was entirely an administrative error on the part of my campaign.
"I very much regret that the donation was not registered as it should have been and I am taking immediate steps to do so."
Mr Mendelsohn, who was not the party's fund raiser at the time, is already facing calls for his resignation after the disclosure that he was aware two months ago of the proxy donations to the party made by property developer David Abrahams.
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