Tony Blair was asked by Scotland Yard detectives to keep silent about his second police interview just four days before Lord Levy, his chief fund-raiser, was quizzed by them about a suspected cover-up in the cash for honours affair.

The police would only cite "operational reasons" for their request to the Prime Minister, who was questioned for 45 minutes last Friday morning in No 10 before he flew to Switzerland for world trade talks.

Like his first interview in December, Mr Blair was questioned as a witness and not under caution. He again had no lawyer present, only a note-taker.

Downing Street stressed that there was no intention to mislead the public about the PM's latest police interview as the six-day news blackout in disclosing it came at the request of the Metropolitan Police.

Neither No 10 nor Scotland Yard would reveal the line of questioning. The police said in a statement: "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."

Intriguingly on Tuesday, Lord Levy was again arrested but this time on suspicion of conspiracy to pervert the course of justice.

Speculation mounted last night that the news blackout was requested to ensure Lord Levy was not alerted to the possible line of questioning detectives might take with him.

Mr Blair's spokesman explained that only a "tightly-knit" group of people knew about the PM's second police interview and it did not include himself.

Jack Straw, at a weekly briefing with reporters, said it was "absolutely proper" for Mr Blair to comply with the police's request to observe a temporary news blackout. To do otherwise, the leader of the Commons argued, would have risked "compromising the investigation".

Asked if the affair was distracting ministers from doing their jobs, Mr Straw insisted: "The business of government is going on and at a pace."

David Cameron used the news of the Prime Minister's second police interview to intensify his call for him to stand down. He said it only confirmed how Mr Blair was a "short-term Prime Minister", whose authority was draining away.

SNP MP Angus MacNeil, whose initial complaint sparked the police inquiry, added: "Mr Blair's situation is looking worse with every passing day. He's questioned and a few days later his chief fund-raiser is rearrested. I'd say this marks another escalation in the police inquiry."

Among the 90 or so people quizzed have not only been Mr Blair but also several members of his inner circle, including Ruth Turner, his "gatekeeper", and thought to include Jonathan Powell, his chief of staff. All deny wrongdoing and no-one has been charged with any offence.