Tony Blair was questioned by police for a second time over cash-for-honours allegations, it emerged today.
The prime minister was questioned for under an hour by officers last Friday, but the police requested an initial news blackout.
News of the interview, which took place without a lawyer and not under caution, only emerged from the prime minister's official spokesman today.
Mr Blair's original interview in December was the first time a serving prime minister had been quizzed by the police
Scotland Yard later said it had requested the news blackout for operational reasons, and that the interview had been to "clarify points emerging from the ongoing investigation".
Today's news follows the re-arrest this week of Lord Levy, the PM's personal envoy to the Middle East and Labour's chief fundraiser, on suspicion of conspiracy to pervert the course of justice.
Lord Levy has denied any wrongdoing, and has been released on bail.
There was initial suspicion that Downing Street had misled reporters by keeping quiet about the interview - conducted before Mr Blair left for the World Economic Forum in Davos last Friday.
But police contacted Downing Street yesterday afternoon and told staff it no longer needed to be confidential.
The Tories renewed their call from yesterday for Mr Blair to go "in the national interest". George Osborne, the shadow chancellor, said: "This government is paralysed. It is difficult to see why Tony Blair is remaining in office."
No 10 said they did not know whether Mr Blair would face further questions, saying that was a matter entirely for the police.
The only people present were the prime minister himself, a Downing Street note-taker and an unknown number of police officers.
The spokesman was unable to say how many police were present, whether they were uniformed or whether they included the man leading the inquiry, Assistant Commissioner John Yates.
Because the police requested that news of the interview should not be made public, members of the Downing Street press office team were not informed until late yesterday, when police said that the blackout could be lifted.
The spokesman declined to say whether anyone else in Downing Street was informed, saying only that the information was "kept extremely tight".
Mr Blair was first interviewed by police last December.
Last month Downing Street aide Ruth Turner was arrested in a dawn swoop on her home, on suspicion of perverting the course of justice. She was released on bail, and Mr Blair expressed his full confidence in her.
The Metropolitan police investigation was first expected to report back before the party conference season last autumn, and then to hand a file to the Crown Prosecution Service before the end of January.
The arrests on conspiracy suspicions, although they have not yet led to any charges, have led MPs to believe the investigation is reaching a head. There has been unconfirmed speculation about dual email systems within Downing Street.
The original allegations centred on a swath of Labour lenders who gave millions to the party before the 2005 general election and were subsequently recommended for honours.
The former Conservative party leader Michael Howard has also been questioned by police - as a witness - as have several members of the cabinet.
When the original complaint was made by the SNP MP Angus MacNeil, the former Downing Street chief of communications Alastair Campbell called it a "passing political hoo-haa".
The 10-month investigation has instead cast a dark cloud over Downing Street as Mr Blair prepares to leave office.
Mr MacNeil said the news marked "another bleak first in British politics".
"Mr Blair's situation is looking worse with every passing day. He appears to be in very deep trouble.
"He's questioned and then a few days later his chief fundraiser, Lord Levy, is re-arrested. I'd say this marks another escalation in the police inquiry."
Mr MacNeil added: "It also gives the lie to suggestions coming out of Downing Street that the police have been leaking, because apparently they asked for a news blackout."
The Liberal Democrats, who earlier this week said the saga now had a "whiff of Watergate" about it, said: "It is clear that this inquiry is going to haunt Tony Blair throughout his last months in office and beyond.
Ed Davey, Sir Menzies Campbell's chief of staff, called on Labour MPs to "stop sniping at the police from the sidelines and allow them to continue to do their job professionally".
Yesterday the chancellor, Gordon Brown, urged people to wait for the "full facts" of the police investigation.