A leading Tory donor has been questioned under caution by detectives investigating the so-called cash-for-honours affair, it was reported last night.
Bob Edmiston, who made a multi-million-pound fortune importing cars, loaned the party £2 million - money he has since said he does not want repaid.
The Times said he was one of a number of rich benefactors questioned as part of the inquiry, sparked by claims that wealthy Labour backers were being rewarded with seats in the House of Lords.
The scope of the inquiry has since been widened to cover similar claims about the Tories.
Scotland Yard said a number of people had been questioned in relation to its inquiries, but would not identify who they were.
Mr Edmiston's was among nominations for a peerage blocked by a watchdog in the summer, although that was in relation to tax issues.
Others interrogated over the affair, although not under caution, include Lord Laidlaw, Lord Ashcroft and Swedish sports equipment tycoon Johan Eliasch, the paper said.
Earlier this week, one of Tony Blair's top aides, Downing Street director of government relations Ruth Turner, was interviewed under caution.
And another key adviser at Number 10 John McTernan - the PM's director of political operations - is also reported to have been grilled by detectives.
Shadow Chancellor George Osborne said he would not comment on a police investigation.
But he said the Tory Party had made an offer to the Labour Party to put a cap on political donations and remove multimillion-pound donations.
"We have been able to raise quite a lot of money under David Cameron because people like what they see in our party," he told Sky News.
"So we are making this offer - it is not not necessarily in our immediate best financial interests - but we think it is right thing to do."
He said the Tory Party was advocating that the shortfall should be made up by the British taxpayer.
The public faced a choice which was not "comfortable" he said, between a system of large donations and all the problems this entailed, and helping to contribute to political parties.