Boris Johnson has been put on notice by his own side

There's no hiding the horror of this result for the Conservatives.

What is unknown is whether the North Shropshire result will, in time, mark the definitive moment Boris Johnson's leadership fell apart. Or whether it confronts the prime minister with the incontrovertible evidence that he must change if he's to survive.

There are plenty of Conservatives, even in the party's senior ranks, who believe it's over.

The question is not whether he will lead the party into the next election, but how and when he will leave, and who will make moves to oust him.

This strand of opinion includes some of his early backers who have reluctantly concluded that when it comes to governing, not campaigning, he cannot, or will not change.

Yet others persist that his talents are significant. If he can reflect honestly on what's gone wrong and make changes, particularly in Downing Street, this moment may represent the bottom of the slide, and Mr Johnson can clamber out.

Rather than close down the stories that caused such damage in this by-election, though, less than 24 hours since the polls closed, another set of claims emerged that stretched credulity.

To try to move on from the cringeworthy allegations about a No 10 party during lockdown, Mr Johnson had asked his top civil servant, Simon Case, to investigate.

The report, it was hoped, would emerge before Christmas, establish the facts, perhaps result in one or two departures from No 10, then the world could move on.

Except as the by-election disaster news percolated, reports began this afternoon that Mr Case's own office had invited 15 people to what was called, on the digital invite, a "Christmas Party".

The man who was in charge of investigating the alleged Whitehall parties turned out, it appeared, to have hosted one of his own.

The Cabinet Office says it was a "virtual quiz" and Mr Case only really passed through. A few staff had a few drinks while at their desks, and no outsiders were involved or invited.

Yet you wouldn't be blamed for feeling this episode was like, yes, an episode of political satire The Thick Of It. One of the plot lines in an episode does in fact involve a political figure launching an investigation into themselves.

Within a few hours of the news emerging, Mr Case had, as if by magic, stepped aside from carrying out the investigation, and it will be carried out by the revered and feared official, Sue Gray.

This could be tough for No 10 because she's likely to investigate without fear or favour. And the change of personnel also diminishes the chances of a quick resolution.

But does it all matter? Plenty of people are furious with what went on. The opposition parties are certainly not going to let up.

You, however, may be thinking who cares if a few people in the Downing Street press office had a few warm white wines 12 months ago?

You may well think, with the surge of the pandemic, surely, there are much better things for politicians to be spending their time on?

Except the two are linked. The conduct and behaviour of those who make the rules matters.

A special kind of rage is often reserved for political hypocrisy, which was displayed in the North Shropshire result.

And it matters, that by their own decisions not to be straight about what happened from the off, or find an investigator without any conflict, Downing Street has failed to take control of the row.

Just as many MPs are desperate for No 10 to get a grip, there is new evidence that the team in there find that desperately hard to do.

And with the pandemic surging, doubts over the prime minister's credibility matter enormously.

• Top civil servant quits No 10 probe over own party

• PM urged to get a grip after by-election rout

Sources have even suggested that some in government had hoped to spend last week "rolling the pitch", preparing the public for a return to much tighter restrictions to control the pandemic, but that didn't happen as hoped because the distractions of the saga of what's been going on under No 10's roof made it politically impossible to do.

I'm told that there were even conversations about putting England's chief medical officer, Prof Chris Whitty, forward for public appearances on his own to separate the political mess from the vital public health message.

In fact Prof Whitty did appear in an ad campaign alone. And it's impossible right now to know for sure if those plans had really existed and were indeed canned.

The pandemic means it's likely the country faces a period of significant disruption.

The Christmas period presents a chance for Tory worries to calm, and the prime minister to reset. But there's no question as Westminster hopes to pack up for a break, this doesn't feel like a government with a majority just shy of 80.

Right now, Boris Johnson doesn't feel like a leader with a majority he can rely on at all.

After a month of mistake after mistake, crowned by a by-election disaster, Boris Johnson has been put on notice by his own side.

Without a visibly new and improved operation in 2022, his time in office may, before too long, be up.