Lord Sainsbury, the Science Minister and a major Labour Party bankroller, and Ian McCartney, the Trade Minister and former party chairman, have already been interviewed by officers from Scotland Yard.
Ahead of today's G8 summit, Tony Blair yesterday refused to answer questions over the police inquiry, while Downing Street also rebuffed queries over whether ministers had access to government lawyers.
At a press conference ahead of the G8, Mr Blair said he would not be diverted by the investigation: "I am not going to comment on those inquiries." He denied his position at the summit would be compromised, adding: "You only have to look at what is happening in the Middle East today to see what I should be concentrating on."
His official spokesman told journalists that he did not want to comment on an ongoing police investigation.
However, MPs are planning to ask ministers to declare whether they will have access to government lawyers, despite the allegations revolving around party political funding.
A spokeswoman for Lord Sainsbury confirmed that he had been questioned by detectives during their investigation into whether or not people have been given honours in return for making financial donations to political parties.
She would not reveal when or where the Parliamentary Under Secretary of State for Science and Innovation had been interviewed but added that he had not been placed under caution.
Mr McCartney had "voluntarily offered" to speak to the police, a spokesman for the Trade Minister confirmed.
"He was interviewed as a witness, but he wasn't cautioned and did not attend a police station," the spokesman said.
In April, a senior official named Mr McCartney as being one of several ministers implicated in the loans-and-honours affair.
So far, nearly 50 officials and ministers have been questioned over the allegations, which were raised to police by Angus MacNeil, the SNP MP for the Western Isles.
The Commons constitutional affairs committee has already invited Alastair Campbell, Mr Blair's former director of communications, to give evidence to their separate probe into honours, but he has refused to co- operate.
A spokeswoman for the Constitutional Affairs Committee said he had turned down an invitation from MPs to give evidence but the committee would not pursue it.
The move is bound to anger some Commons authorities and MPs, who believe that Parliament should use its right to compel witnesses to appear before committees.
Meanwhile, John McDonnell, a veteran Labour rebel, confirmed he would stand against Gordon Brown when the Prime Minister stands down.
"Spin and allegations of sleaze are causing decent people to lose trust in our party," he said.
Mr McDonnell denied that he was standing as a "stalking horse" to try and force a leadership election, but stressed he wanted Labour members to have an alternative to New Labour.
WITH his strong accent and ties with the unions, Ian McCartney is a rare commodity in a New Labour Cabinet.
The Dunbartonshire-born politician, a close ally of John Prescott, was demoted from Labour Party chairman to trade minister as part of Tony Blair's ruthless reshuffle in May. The 55-year-old Makerfield MP was one of several Brownites to lose their jobs.
He was first elected to Parliament in 1987 and he was appointed minister without portfolio and Labour Party chairman in 2003.
Mr McCartney is seen within the government as an important negotiator and key link with grass-roots supporters.
Last October, Mr McCartney - who describes himself as the "Socialist MP for Makerfield" - underwent open heart surgery.
WITH an estimated fortune of between 1 billion and 2 billion, stemming mainly from his family's supermarket empire, Lord Sainsbury of Turville has been able to spend money generously on his twin passions, science and politics.
In the 1980s Lord Sainsbury's political affiliations lay with the Social Democrats. However, following the demise of the SDP/Liberal Alliance, he switched his loyalty to Labour.
According to reports, the billionaire businessman has donated more than 10 million to the party since 1999.
Lord Sainsbury was made a life peer in 1997, following Labour's election victory, and in July 1998 was appointed parliamentary under-secretary of state at the DTI .