Cabinet minister Peter Hain has apologised for failing to register some of the donations given to his Labour deputy leadership campaign.
Mr Hain says he will report to the Electoral Commission this month
The Work and Pensions Secretary said he blamed "administrative failings", which he described as "deeply regrettable".
Although he declared donations of £82,000, the Guardian newspaper claims the real figure may be over £100,000.
Mr Hain said he had undertaken a full audit and would be providing the details to the Electoral Commission.
The Neath MP, who is also Welsh Secretary, revealed at the end of November that he had failed to register a £5,000 donation from Jon Mendelsohn, Labour's chief fundraiser.
Then at the beginning of December, Mr Hain said other donations to his campaign "were not registered as they should have been", including a £1,300 campaign dinner.
At the time, he said he was reviewing all campaign donations and would be submitting a full declaration to the Electoral Commission.
The Guardian claims Mr Hain discovered that no donations had been registered after 4 May last year - six weeks before the deputy leadership contest ended.
In a fresh statement following the Guardian's allegations, Mr Hain said: "As I said in December, as a result of administrative failings within my campaign there were donations to my deputy leadership bid which were not registered within the normal time, to the Electoral Commission.
"Since December I have undertaken a full audit of all donations to the campaign and have agreed with the Electoral Commission to provide the details of these late declarations to them, by the middle of January.
"I reiterate that this is deeply regrettable and I sincerely apologise."
Steve Morgan, who chaired Mr Hain's deputy leadership campaign, told BBC Radio Wales: "The issue here is how will all of us manage with donations that come into a campaign after the campaign has officially closed down?
"Peter has been very open about this whole process - more so than most - and I think he's been fully co-operative with the Electoral Commission over some of these key issues, which none of us have experienced before. Donations in kind being one of them."
The Electoral Commission told the BBC that it has discussed the campaign's donations with Mr Hain personally and with his office.
However, it would not confirm whether a date had been set for the re-submission of the accounts.
Meanwhile, a spokesman for Mr Hain has confirmed that he took a donation from Welsh finance company Picture Financial Services, which features an endorsement from him on its website.
Mr Hain congratulated the firm in August 2005, in his capacity as Secretary of State for Wales, for creating 200 jobs. Then 14 months later, its chief executive Neville Allport, gave a donation to Mr Hain's deputy leadership campaign.
A spokeswoman for the company says that he gave the money in a personal capacity and had not been approached by Mr Hain's team for the donation.
Mr Hain's spokesman strongly disputes any suggestion that the donation was linked to the endorsement and said it was normal for the Welsh Secretary to congratulate companies in this way.
BBC political correspondent Laura Kuenssberg said Mr Allport had been an acquaintance of Mr Hain's for several years.
Mr Hain was one of six contenders for Labour's deputy leadership, which was eventually won by Harriet Harman.
A police inquiry is under way into proxy donations of more than £650,000 given to the Labour Party by property developer David Abrahams since 2003.
Mr Abrahams' donations broke electoral law because people must use their own names when giving more than £5,000 to political parties.