The chairman of IT services company Capita has been named as one of the individuals who loaned a total of almost £14m to the Labour Party's election fund last year.
An investigation was launched into the loans after Labour treasurer Jack Dromey went public last week, saying he did not know the party had borrowed the money from 12 supporters.
The list shows Capita chairman Rod Aldridge gave the Labour Party a commercial loan of £1m.
Aldridge's donation has come under scrutiny in the media because Capita runs many high-profile government IT projects, including the London Congestion Charging scheme, TV licensing and the Criminal Records Bureau.
There is no evidence of any link, however, and Aldridge said in a statement that the loan was made in a personal capacity and has nothing to do with Capita.
He said: "The Labour Party came to me last year in need of financial support following the costs incurred at the last general election. As a member of the party, I was pleased to help. This was a personal decision on my part."
The one-year £1m loan was made at a commercial rate and Aldridge said he fully expects it to be repaid with interest.
The Labour Party said that under Electoral Commission rules there is no legal requirement to disclose commercial loans made to political parties.
A party statement said: "The loans were given and received in good faith, and would have been registered in the appropriate way in our annual accounts."
The party's National Executive Committee is expected to propose today that all future commercial loans agreed by Labour be declared publicly, including their sources.
The list of backers also includes Gordon Crawford, chairman of London Bridge Software - which develops debt collection and credit management applications — who lent the Labour Party £500,000.