Key evidence over honours still secret, says Met

The "most significant" evidence uncovered by the abortive 19-month investigation has still not become public knowledge, the Met's official report into the affair revealed.

The report, published today ahead of a meeting of the Metropolitan Police Authority next week, also shows that detectives considered quizzing Tony Blair as a suspect and not just a witness.

It dismisses claims by Mr Blair's former fundraiser Lord Levy that his arrest was driven by anti-Semitism and points out that several witnesses were uncooperative.

The report lists a number of "key issues" which arose during the inquiry, including the decisions to interview Mr Blair on three occasions. It is understood that police were warned the Prime Minister might have to quit if he was questioned as a suspect.

It also points out that police had to request a "forensic image of the No10 computer server", retrieve emails from the Cabinet Office and request statements from members of the 2005 Cabinet.

There were reports that detectives had concerns that incriminating emails may have been concealed or sent through a "hidden" system.

Despite a series of revelations emerging in the media, the most explosive details remain a closely guarded secret, according to Scotland Yard.

The report by the Operation Ribble team defends the £1.43 million probe as "focused and proportionate", and also criticises the Electoral Commission directly for failing to provide "robust oversight" of the legal rules governing loans to political parties.

The document, written by Detective Inspector David Jones, could also increase pressure on Met Commissioner Sir Ian Blair, by indicating that he did have a role in overseeing the probe from the outset, despite claims he was kept at arms length.

Although there was "no need" for Sir Ian to be involved in "specific tactical decision making", the report says it was " unrealistic" for him to be kept completely out of the inquiry - partly because he had " regular meetings" with individuals who might be "either witnesses or suspects".

Dismissing allegations of leaks from the inquiry, the report states: "No material was leaked to the press from within the investigative team."

The Operation Ribble team still believes that the investigation obtained " considerable evidence", while accepting the decision of the CPS this summer not to bring any charges, according to the report.