The Conservative Party has announced it will publish a list of wealthy individuals to whom it owes money.
The loans were made before David Cameron became party leader
But secret loans made before the last election, which have since been repaid, will not necessarily be revealed.
Labour has provided its list of lenders and has been pressing the Conservatives to do the same.
Tory leader David Cameron has announced he is meeting Tony Blair on Monday to discuss party funding. He also called for a cap on political donations.
Mr Cameron told the BBC: "I've asked the party over the last few weeks to sort this out... Some loans have been repaid... some people have turned loans into donations".
The party will also reveal all donations it has received since Mr Cameron became leader last year.
The announcements come after it emerged the police investigation into "cash for peerages" had been widened.
The Metropolitan Police said the inquiry, which initially focused on Labour, had become a cross-party probe.
It refused to say which parties were being investigated but it has emerged that Labour MP Rosemary McKenna has asked the force to look at the Tories too.
It is understood Scotland Yard's specialised crime directorate is also looking at claims about at least one other party.
Amid pressure to show the source of about £18m in loans, the Conservatives have been approaching lenders to ask if they can make their names public.
One lender, who had been told the list would be out on Friday, said the names were all familiar existing and former donors.
"None of the names will cause the party the slightest embarrassment," he told BBC News.
He said a number of lenders had agreed to convert their loans to gifts, which have to be declared by law.
It is not yet clear how comprehensive the list will be and what time period it will cover.
All the political parties and the people who have lent or donated money have denied any favours were given for the loans.