At least two ministers have been questioned by police as part of the "loans for peerages" inquiry.
The two ministers were not cautioned, say their spokesmen
Neither Science Minister Lord Sainsbury nor Trade Minister Ian McCartney was cautioned before the questioning, say their spokesmen.
Supermarket millionaire Lord Sainsbury is one of Labour's biggest donors and lent the party £2m before the election.
Mr McCartney was Labour chairman before the election and signed nomination forms for the party's new peers.
He was reportedly in hospital at the time, recovering from a triple heart by-pass operation.
Questioned after talks with Canadian Prime Minister Stephen Harper, Tony Blair said he was not going to comment on the ongoing police investigation.
He insisted his work at this weekend's G8 summit in Russia would not be compromised by the inquiries coming close to Downing Street.
Instead, he would concentrate on problems in the Middle East, climate change, and energy security, he told reporters in Downing Street.
Mr McCartney's spokesman said the minister had spoken voluntarily to the police in the past few weeks. He had not gone to a police station and was not interviewed as a suspect, the spokesman added.
It was part of the "process of co-operation" with police, he said.
Lord Sainsbury was cleared of breaching the ministerial code in April after failing to disclose a £2 million loan to the Labour party.
He apologised and said he had confused the loan with a £2m declared donation he had made.
Meanwhile, Labour fundraiser Lord Levy has called his own arrest unnecessary and "entirely theatrical".
Lord Levy, was questioned on Wednesday and Thursday. He denies any wrongdoing.
Police are investigating all the main parties to see whether people have been given honours in return for making financial donations.
Prime minister's questions?
The investigation was launched after it emerged that some people nominated for peerages by the prime minister had given large secret loans to Labour last year.
All concerned deny any wrongdoing. The rules on political funding meant that loans on commercial terms did not need to be disclosed publicly.
On Thursday, Met Police deputy assistant commissioner John Yates privately told the Commons public administration committee his team had so far questioned 48 people, 13 of them under caution as part of the investigation.
Committee chairman Tony Wright told journalists he thought Mr Yates "would not baulk at interviewing anyone else".
That has increased speculation that police could question Mr Blair.
But the prime minister's official spokesman on Friday confirmed that the police had still not asked to interview the prime minister.
He would not say whether or not any Downing Street officials had been approached.
"We don't comment on police investigations, full stop," he said. "That's the right and proper approach of the government."
Conservative leader David Cameron on Friday said the "cash for peerages" claims were "extremely serious".
Asked about the fact that more Conservative than Labour figures have been interviewed by the police, he said: "The police must go ahead with their inquiries in the way they see fit".
He said claims that Tory peerages could be bought for half a million pounds were "ridiculous".
And he pointed out that he had not put forward any lists of peers since he became leader last year.