‘Wait for Sue Gray’ was the ministerial mantra last week. And wait, we all have, as the days have ticked by with no sign of her report into the lockdown parties allegedly held at No. 10. But now, after a week of stasis which has had Westminster on tenterhooks, Cressida Dick and the Met police have dropped another bombshell on a quiet Friday morning.

Dick revealed on Tuesday that her officers would be launching a criminal investigation into ‘partygate,’ having previously ignored all calls to do so. And today the Met has issued a fresh statement, saying they want ‘minimal reference’ in Gray’s report to the No.10 parties which they’re investigating. At least why we now know why she still hasn’t published…

The Met add – euphemistically – that they have had ‘ongoing contact with the Cabinet Office’ including on the ‘content of the report, to avoid any prejudice to our investigation.’ This does of course leave Gray in a quandary: does she go ahead and publish her incomplete report, without the details of the most serious potential breaches but which could have HR consequences?

Or does she put the whole process off until after the Met’s police investigation is complete? The former would risk being branded a whitewash; the latter would buy Boris Johnson some much-needed time for some desperately-needed party management. Either way today’s intervention is seen as a helpful one for a PM who needs every bit of luck he can get.

It isn’t exactly clear why a factual civil service report about events the police is investigating would ‘prejudice’ the police’s investigation. Normally the idea of prejudice is invoked in the context of preventing details that might sway a jury in the event of a trial. But police don’t normally ask journalists not to report on ongoing investigations before such matters have gone to court.

And, moreover, why has it taken until now for the Met to announce their instructions to the Cabinet Office? A week ago they denied any investigation was needed; three days ago they announced a probe had been launched but didn’t explain how this would impact Sue Gray’s report. What will be the line tomorrow?

No wonder many in Westminster are asking: what exactly is the Met doing?