Prime Minister Tony Blair was questioned for a second time by police investigating cash-for-honours allegations, it has emerged.
Mr Blair: Was questioned before flying to Davos
The interview, which lasted 45 minutes, took place at No 10 last Friday and was kept secret at the request of police.
Previously questioned in December, Mr Blair was again treated as a witness.
Police are investigating whether cash was donated to political parties in exchange for honours. All involved in the claims have denied any wrongdoing.
Constitutional Affairs Minister Harriet Harman told BBC One's Question Time the whole cash-for-honours inquiry had "eroded trust" and was "unfortunate to say the least".
Mr Blair's official spokesman said the prime minister had not been interviewed under caution and was not accompanied by a lawyer - although a civil service note-taker was present.
Scotland Yard said the news blackout had been requested for "operational reasons", but gave no further details.
It added: "The prime minister has been interviewed briefly to clarify points emerging from the ongoing investigation. He was interviewed as a witness, not as a suspect and co-operated fully."
On Tuesday Labour's chief fundraiser Lord Levy, who is also Mr Blair's Middle East envoy, was arrested for a second time by police investigating the claims, this time on suspicion of conspiracy to pervert the course of justice.
The BBC has learned that he was asked about notes of meetings at which he is believed to have discussed honours with senior Downing Street staff.
It followed the arrest just over a week earlier of Downing Street aide Ruth Turner, on suspicion of perverting the course of justice.
Neither has been charged but it sparked speculation that the police had not been given all the information they needed.
Other members of Mr Blair's inner circle have also spoken to the police.
At prime minister's questions on Wednesday, SNP leader Alex Salmond asked: "Is there a cover-up in Downing Street?"
Mr Blair replied that for "obvious reasons" he could not make any comment.
The secrecy of Mr Blair's interview was such that the whole press team at Number 10 had not known it had taken place, his spokesman said.
Commons leader Jack Straw said it was "absolutely proper" that Mr Blair had complied with the police request for a news blackout.
The cash-for-honours inquiry began after it emerged that large secret loans had been made to Labour before the 2005 general election, and that some lenders had subsequently been nominated for peerages.
It was widened to cover the other main parties, with former Conservative leader Michael Howard among those questioned.
It also appears to have widened in scope, from the original laws against selling honours, to whether anyone has attempted to pervert the course of justice during the police inquiry.
SNP MP Angus MacNeil, whose complaint prompted the police inquiry, said it was "another bleak first in British politics".
And Liberal Democrat spokesman Edward Davey added: "It is clear that this inquiry is going to haunt Tony Blair throughout his last months in office and beyond."
Tory leader David Cameron said: "Obviously it's serious when a serving prime minister is questioned by the police twice. But I think we should wait for the outcome of that investigation."
He added that the government was in paralysis while it waited for Mr Blair to resign.
Attorney General Lord Goldsmith has refused to stand aside on the grounds that he could not avoid his legal obligation to give his personal consent to prosecute in certain serious cases.
However he has pledged that if he is consulted by the Crown Prosecution Service he would appoint an independent senior counsel to review all the relevant material and to advise him.
He told BBC Radio 4's PM: "I've been enormously flattered by the number of times people have described me as a close friend of the prime minister. Who wouldn't be?"
He added: "I don't think I am; I doubt very much that he would regard me as such."
Asked if people would find it "absurd" that he could have a hand in the decision to prosecute, he said: "Let's see what if anything happens.
"I know no more than anyone else: I am not in touch with the police; I am not being kept in touch with the inquiry; I only know what I read in the newspapers."
About 90 people have been interviewed during the inquiry so far. No one has been charged and all involved deny any wrongdoing.