Tony Blair was questioned at 11am on Thursday by police investigating cash for honours allegations but it was said that he had not been cautioned before the interview. He was also not accompanied by any lawyer.
The probe that began after it was revealed that Labour was given secret loans ahead of last year's election and indications were that he would be asked about the loans as were some donors who were subsequently nominated for honours. Assistant Commissioner John Yates, of Scotland Yard, has said he expects to deliver a report to the Crown Police Service next month.
Blair's spokesman said the two-hour interview was held after the weekly Cabinet meeting. The Prime Minister explained to police why he had nominated each one of the people he had put forward for a peerage. There is no indication so far of whether police will want to talk to him again.
The inquiry was initiated following a complaint from the Scottish National Party, and then widened to include other main parties. "Given that the SNP made the complaint about people nominated for peerages by the Prime Minister you would expect that the police would ask to see the PM as their inquiries come to a conclusion," the PM's spokesman said.
About 90 people have been interviewed by the police. All deny any wrongdoing. BBC Political Editor Nick Robinson said it was an extraordinary development but one that had been expected for some weeks. But he added the fact that Blair was not interviewed under caution was significant as it implied that police did not intend to bring any charges against him. It was however an embarrassment for the prime minister who had promised to make politics "whiter than white" when he came to power in 1997.
Analysts however pointed out that the very fact that a Prime Minister in office had been interviewed by itself was an extraordinary development. "It hardly needs stressing just how serious it is for the government and the Labour Party. And the fact it has been taken so seriously by the police has already seen the government facing allegations it is just as sleazy, or worse, as the Tories were in their darkest days under John Major.
It is also hugely embarrassing for Blair as he nears his departure from Downing Street. At worst, if any wrongdoing is found, it could both hasten and mar that end. His planned departure has already been marked by in-fighting and a failed coup and he has been forced to announce he will be gone by next summer.
But, despite all that, there are still demands for him to go now. The police interview could end his hope of controlling the timing and manner of his departure.
In his last weeks and months, and after final appearance at the Labour party conference in Manchester as leader and prime minister, he has been drawn into this unprecedented police inquiry. But it must be remembered that the other parties are also being investigated, with former Tory leader Michael Howard already interviewed as a witness by police.
Blair had declared, "Nobody in the Labour Party to my knowledge has sold honours or sold peerages", but he also said he took ultimate responsibility for what might have been done by the Labour party. "The buck stops with me".
It is very much possible that after all, the police might not find any evidence of wrongdoing. That will clear the cloud hanging over the prime minister, the government and the Labour party, but it is inevitable the affair will leave a bad taste behind it.
But the worst scenario could be that police found offences had been committed. The consequences for the government would be devastating and it would be impossible for Blair to survive that. And Blair was still in Downing Street at the time, he would be expected to take the blame and resign.