One of the odder claims doing the rounds in Westminster is that the announcement that the Metropolitan Police is investigating potentially illegal pandemic parties in Downing Street somehow diffuses Boris Johnson’s political troubles and relieves the pressure on him. 

This counterintuitive argument is being pushed by Mr Johnson’s inner circle, who say that since the PM vehemently claims his innocence, and thinks the outcome of the investigation can only fall in his favour, only this full police probe can exonerate him and draw a line under the matter satisfactorily in the eyes of the public.

Over optimistic? Possibly. Desperate? Maybe. But these are unprecedented times.

Live reaction and fallout as police investigation launched – politics latest

A clean bill of health from the Metropolitan Police and Sue Gray inquiry is just one possible outcome of the maelstrom that Mr Johnson finds himself in – almost every other outcome from the probes and inquiries into his behaviour would be worse.

Several of them could end up with him being ousted from office sooner or later. Despite the bravura poise he adopted in the Commons during a statement on Ukraine, this remains a moment of maximum peril for Mr Johnson.

There are now three main ways Mr Johnson’s premiership could potentially end.

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The first is a fatal blow in the Sue Gray report, which may come in the coming hours or days, and opinion in the Conservative party settling firmly on the idea he must exit Number 10.

The second is the police sanctioning Mr Johnson personally at the conclusion of their investigation, which would also make it hard for Tory MPs to offer their continued support.

The third is that Tory MPs, who will play a role whatever happens, decide the weight of problems facing the prime minister make him certain to be an electoral drag in future elections.

This does provide a crack through which Mr Johnson could yet climb to reset his premiership, but having lost the confidence of the Scottish party, many of the MPs in the new intake, and some of his party grandees this is an uphill task.

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Read more: Boris Johnson willing to be interviewed by police but does not think he has broken law – No 10

The Metropolitan Police inquiry into Mr Johnson is likely to take several weeks at least, which elongates the period before Tory MPs can draw a line under the issue. The Sue Gray report is expected much sooner, but the mood in Whitehall has been darkening for days.

For those wondering if things could get worse, there are signs they could.

Sky News understands that Ms Gray has been handed photos of Boris Johnson at an event in Downing Street with wine bottles, which suggest revelry against the spirit and letter of pandemic lockdown law. It is unknown whether such images will be published in the final report, but two different sources confirm their existence. For some wavering backbenchers that might be problematic enough.

To underline how rapidly things are moving, the discussion among Tory MPs appears to have already moved beyond questions like who might run for leader, and whether Mr Johnson should stay on.

Instead many are already talking about how the change should happen. Should frontrunner Rishi Sunak do a deal with fellow favourite Liz Truss, for instance, to avoid a bruising contest and speed things along? Would guaranteeing her a great office of state in return for not running against him be enough? Would a less obvious candidate serve the party better?

These are not questions Boris Johnson wants people asking, but they already are.

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