Police investigating cash-for-honours allegations have asked up to five Cabinet ministers for interviews.
Police are investigating whether donors received honours for cash
Health Secretary Patricia Hewitt has confirmed she was among them. Ex-Cabinet minister Alan Milburn has already been interviewed.
According to one minister, police said they wanted "to learn about the way the honours system normally works".
Police are investigating whether donors received honours in return for cash. All involved deny wrongdoing.
The probe began after it was revealed all three main parties were given secret loans ahead of the last election.
It now appears many, if not all, of the members of the Cabinet at around the time of the 2005 general election, apart from Tony Blair, have received letters from or been contacted in some other way by detectives.
In a statement, Mr Milburn, the former health secretary and Labour's one-time election supremo, said: "Following a request from the police, I have been interviewed as a witness.
"The police stressed I was not a suspect, and the interview did not take place under caution."
Chancellor Gordon Brown and Deputy Prime Minister John Prescott are among those to have been contacted about the loans, worth £14m, made before the 2005 election, it emerged earlier.
Others known to have been contacted include Jack Straw, John Reid, David Miliband, Alan Johnson, Peter Hain and Ruth Kelly.
BBC political editor Nick Robinson said it appeared that not all ministers had received the same letter.
One Cabinet source said they were simply asked if they were involved in any way in certain peerage nominations.
But another said they were also asked about their knowledge of any loans secured by Labour before the election.
The Scotland Yard officer in charge of the investigation, John Yates, has previously told MPs "you go where the evidence takes you".
Our correspondent said it was for this reason that friends of Mr Blair expect him to be interviewed - possibly under caution - in the weeks to come.
But they insist the prime minister has had no contact with the police as yet.
Police are thought to have spoken to, or contacted, more than 50 people, including some of Mr Blair's closest advisers, and, from the Conservative side, former leader Michael Howard.
A Conservative spokesman said on Wednesday no other shadow ministers had been contacted by police.
For the Lib Dems, Norman Lamb said: "The entire business has undermined public confidence in the political system."
Director of Public Prosecutions Ken Macdonald - a former colleague of Cherie Blair - and Metropolitan Police Commissioner Sir Ian Blair, have decided to stand aside from decisions related to the investigation.
Attorney General Lord Goldsmith - who attends Cabinet and who is close to Mr Blair - on Tuesday said he would not stand aside from the process but promised to act "in the interests of justice".