Boris Johnson braced for perilous 48 hours with release of Sue Gray’s report

Boris Johnson is braced for the most perilous 48 hours of his premiership, with exasperated Conservative MPs due to see an official report into Downing Street parties that has now triggered a criminal inquiry.

The Metropolitan police commissioner, Cressida Dick, announced on Tuesday that her officers are investigating allegations of law-breaking at the heart of government on the basis of evidence unearthed during an inquiry by the senior civil servant Sue Gray.

Former No 10 staffers told the Guardian that the police inquiry will uncover evidence which has not yet been submitted to Gray. One senior Tory said the Scotland Yard inquiry was a "different ballgame", adding: "Officials who don't tell Sue Gray the whole truth will not hold back from the cops."

Downing Street sources refused to be drawn tonight on whether the prime minister could give the green light for the report to be released as soon as Wednesday, but it is certainly expected within days.

A senior government source cautioned it was unlikely to be published in full, saying: "You don't need to be a lawyer to realise that if there's an ongoing police investigation, there are constraints on what you can publish."

Gray has interviewed witnesses and examined key evidence including security logs showing who was in Downing Street and when. She is also thought to have been shown photographs of parties though Cabinet Office sources stressed these were unlikely to be included in the report.

It is understood the Met's decision to investigate a number of parties in Downing Street and Whitehall was made on Sunday. Johnson had been informed in advance but opted not to tell his cabinet at their weekly meeting on Tuesday, leaving them to find out as they emerged and triggering consternation.