In a case that has embarrassed the Labour government, Hain failed to declare 103,000 pounds of political donations.
"The notion that there was some attempt by me to hide anything is absurd," said Hain, who used the money -- plus 82,000 pounds that he did declare -- to finance an unsuccessful bid last year to become deputy leader of the Labour party.
The Hain case follows a party funding scandal and a string of government administrative blunders that have damaged the Labour party and left it trailing the Conservatives in opinion polls.
In a statement to reporters, Hain said "poor administration" by his campaign team was to blame for the failure to declare the cash, and said he was happy for parliamentary inquiries into the donations to take their course.
"Meanwhile I will get on with my cabinet jobs," he added.
Pressure mounted on Hain after Conservative deputy David Davies made an official complaint on Friday to parliament's sleaze watchdog, the Parliamentary Commissioner for Standards, that there had been a "very clear breach of the rules."
Hain said in November that he had failed to register a 5,000-pound donation to his deputy leadership campaign because of an administrative error.
But on Thursday he admitted his campaign team had failed to declare donations totalling more than 103,000 pounds within the period required by electoral rules.
He said he met the Electoral Commission on Thursday and provided full details of the donations.
Hain, who raised more in donations for his campaign than any of his five rivals, said he had been concentrating on his ministerial duties and had relied on campaign team officials to comply with election rules.
