Four major donors to the Conservative Party have been questioned by police investigating "cash for peerages" claims, it has emerged.
The inquiry is looking into whether peerages were offered for cash
They include a businessman whose nomination for a peerage last autumn was blocked by the body which vets appointments to the House of Lords.
Robert Edmiston, head of IM group, was questioned by police in July.
The Tories say three other donors - Lord Laidlaw, Lord Ashcroft and Swede Johan Eliasch - were also interviewed.
Mr Edmiston lent the Conservatives £2m before last year's general election but has since converted the loan into a donation.
The Conservative Party said none of those interviewed had been questioned again by the police.
'Clean up' plans
It is understood that nobody employed at Conservative HQ has been interviewed in the inquiry.
Shadow chancellor George Osborne told BBC Radio Five Live: "The story is actually something about something that happened many months ago.
"And we're not in the position that the Labour Party are in, where people who are working for the prime minister have been arrested, and a big Labour donor has been arrested."
Mr Osborne said the Tories had put forward a package of reforms to how political parties are funded to help "clean up" British politics.
Cash for peerages claims
The investigation is looking into whether peerages were offered in exchange for cash, after it was revealed that all three main parties were given secret loans ahead of the last election.
The probe began after it emerged that four businessmen who gave Labour £4.5m in unpublicised loans were subsequently nominated for peerages.
The scope of the inquiry was extended to cover similar allegations involving the Tories.
The party borrowed £16m from 13 wealthy backers.
Last month Ruth Turner, the director of government relations at No 10, was questioned by police.
Three arrests have been made, although all have denied wrong-doing.
Head teacher Des Smith, who was on the council of the Specialist Schools and Academies Trust, was the first person to be arrested and bailed, in April.
Officers have also twice interviewed Lord Levy, Labour's chief fundraiser and Tony Blair's personal representative in the Middle East.
Biotech boss Sir Christopher Evans said he was "shocked and dismayed" to have become the third man arrested.