The names of all those who have loaned the Conservative Party money will be given to the elections watchdog, a senior Tory has said.
The party had insisted it would not disclose the names of two of its benefactors, understood to have loaned money on condition of anonymity.
But Theresa May, shadow leader of the Commons, told the BBC the Electoral Commission would be shown a full list.
However, the names would not be made public, she added.
"As I understand it, the Electoral Commission will be able to see all of the names," she told the Sunday AM programme.
"Obviously there are those who wish to remain confidential in a public sense. But the electoral commission will be able to come in and look at the terms of those loans and the names."
Conservative head of policy Oliver Letwin said the party was determined to help the commission in any way it could.
"Whatever the commission wants to do to satisfy itself that everything is in conformity with the law, the Conservative party will assist it to do."
The Conservatives still owe £16m to 13 more supporters who helped bankroll the last general election campaign.
The party's biggest individual lenders are former treasurer Lord Ashcroft, with £3.6m, and Lord Laidlaw, with £3.5m.
The Conservative Party owes £37m in total, having borrowed nearly £16m from a bank to buy the freehold on its former headquarters in Smith Square and £4.7m from local associations.
The Electoral Commission is calling for more detailed information about loans from all political parties.
Labour published its own list - totalling nearly £14m - nearly two weeks ago, following claims - denied by Tony Blair - that it was selling peerages.
However, Science Minister Lord Sainsbury said there had been some confusion over a £2m loan he made to the party and a separate £2m donation a month earlier.
Downing Street said on Sunday that an inquiry by Lord Sainsbury's permanent secretary had cleared him of breaking the ministerial code.
Transport Secretary Alistair Darling told BBC One's Sunday AM with Andrew Marr he wanted a quick agreement on political funding.
"The best way of dealing with the funding of political parties is to be completely open and transparent and then people can judge for themselves whether they approve or disapprove."
Meanwhile, a Metropolitan Police investigation into "cash for peerages" allegations, which initially focused on Labour, has widened into a cross-party inquiry.