IT’S not a crime to laugh.

It’s not a crime to rehearse.

It’s not a crime to josh with workmates.

But Allegra Stratton and her public relations team did commit an unpardonable crime that finally forced her resignation yesterday.

Not lying to the public. Let’s not be so naïve. Britain is way past getting upset about lying in high places – or even “public servants” breaking rules they design for everyone else.

It’s the new normal.

Give the tittering top team their due. Boris Johnson’s communications team was actually so professional, that it spent time and resources rehearsing porkies to produce the most convincing, bare-faced lies.

No, Ms Stratton’s fatal mistake was the oldest in the book – she got caught.

The National: Allegra Stratton

The video leaked to ITN News at Ten proved that the senior media adviser to Number 10 knew there’d been a Covid rule-breaking party in Downing Street last December and was prepared to lie about it if questioned.

Not surprising really when her erstwhile boss has turned lying into an art form – lying about the economic damage of Brexit, lying about Tory party donors becoming peers and lying about crony Covid contracts dished out to pals.

Why would a relatively low-grade porkie about a “business meeting without social distancing” sound the alarm bells for Johnson’s staff?

Stratton’s basic mistake was allowing her shameful, gigglefest rehearsal to be recorded and saved on to a discreet hard-drive for later use against her by a less than whole-hearted Team Boris member who has risked their career to leak the tape.

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Perhaps there’s more where that came from.

Gaffe Number Two was Stratton’s own bad luck – having a boss whose deepest instinct is to lie (badly) under pressure and thus make things infinitely worse.

Johnson’s performance during Prime Ministers’ Questions was woeful – a masterclass of evasion, buck-passing and poorly executed attempts at distraction which transformed the crass press rehearsal tape from a survivable moment of bad judgement by juniors to a non-survivable offence against the memory of all who died during Covid. Particularly the 489 folk who succumbed that December party day – many of them alone, scared and without family.

So, the question now – can Boris survive it? I suspect not.

Ironically, there was a get out of jail card for Boris to use.

Government buildings like 10 Downing Street are actually exempt from the Covid restrictions imposed via the 1984 Public Health Act. Perhaps Boris was referring to this “exempt status” when he said “no rules were broken” at the Downing Street party. Which still might not have happened.

But it’s far too late to use a technical excuse now.

Boris has been skewered by his only reliable character trait – a resolute refusal to take responsibility for actions.

And everyone can see it. Even Baroness Ruth Davidson.

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As Johnson scuttled early from the Commons chamber yesterday to avoid points of order by Ian Blackford and others, she tweeted: “None of this is remotely defensible. Not having busy, boozy not-parties while others were sticking to the rules, unable to visit ill or dying loved ones. Nor flat-out denying things that are easily provable. Nor taking the public for fools. And today’s ‘we’ll investigate what we’ve spent a week saying didn’t happen and discipline staff for rules we continue to say weren’t broken. was pathetic.

“As a Tory, I was brought up to believe in playing with a straight bat. Believe me, colleagues are furious at this, too.”

Including her successor Douglas Ross who said: “If the prime minister knew about this party last December, knew about this party last week, and was still denying it, then that is the most serious allegation. There is absolutely no way you can mislead parliament and think you can get off with that. No one should continue in their post if they mislead parliament in that way.”

Wowser.

It’s just a shame the punchy Ross statement ended with the damp squib of a supplicant – Dougie “still has confidence in the prime minister to lead the country”.

How that works is entirely beyond me.

The Ross Family are doubtless off the Downing Street Christmas Card list, and yet this half-hearted “stand” will not save him at the next General Election, if recent opinion polls are correct. Indeed, whilst Dougie did stand down as Scotland office minister after Dominic Cummings’s lockdown-breaking trip to Barnard Castle, one can’t help thinking the prospect of losing 11 Scottish Tory seats (including his own) helped focused his mind wonderfully.

In addition to which, it’s clear that Partygate is only going to get worse.

Former Tory Minister Baroness Warsi tweeted yesterday that everyone connected with the cheese, wine and Secret Santa “not party” should resign. Which could prove kinda awkward since Number 10 refuses to say if Cabinet Secretary Simon Case was also a guest at the party he’s set to investigate.

Looking on the bright side, I suppose he will have a fairly accurate guest list.

But seriously, Boris can’t afford to put another foot wrong.

Because in addition to his cynical attempt at diversion last night – bringing England up to the Covid restriction levels adopted in Scotland some time ago – there are even more problems waiting in the wings.

The next scandal could be over cocaine found in Commons’ bathrooms.

Yip, unbelievably 11 out of 12 loos tested in the Mother of Parliaments contained traces of cocaine – including bathrooms beside the private offices of Boris Johnson and Priti Patel. Speaker Lindsay Hoyle has vowed to investigate and call in the police and if rumours of widespread drugtaking amongst senior Whitehall staff are borne out, that could be devastating for an increasingly unpopular Johnson.

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Two separate snap polls published last night show more than half of voters think he should resign as prime minister, including a third of Tory voters in 2019.

Lying at the despatch box is a resigning matter. So, if new evidence proves Boris did know about the December 18 party – or the one held in his Downing Street flat on November 13 (according to that unreliable oracle Dominic Cummings), then Boris will be toast.

And you’d have to say the probability of someone clyping is now extremely high.

Number 10 staff thrown under the bus might “do a Cummings” and reveal all. Likewise senior staff with a conscience who’ve been coming forward to testify against the omnishambles in Westminster. Folk like the whistleblowing former diplomat who revealed appalling levels of chaos in the Foreign Office during the botched evacuation of Kabul.

As those who recall the political demise of Mrs Thatcher can testify, when the Grey Men of the Tory Party finally get active, the end can be swift.

Of course, Boris still has his supporters – Sir Charles Walker MP says Covid was a “hard taskmaster and people can’t get be expected to get it right all the time”.

WATCH: Glaswegians give their verdict on Boris Johnson's Christmas party scandal

Really? Folk awaiting prosecution for holding lockdown parties won’t buy that.

Folk who got it right every time to protect family members won’t either.

Ditto Scots who experienced a very different type of leadership throughout the lockdown and beyond.

Barring one quick maskless pop into a bar during a funeral – for which she immediately apologised – Nicola Sturgeon did comply with Covid restrictions all the time and sacked key staff who didn’t.

So, there might yet be a sudden Al Capone style ending for Boris Johnson.

And you’ve got to say. With a 55% poll lead for independence, the First Minister’s timetable for indyref2 may be looking hard to achieve – but it’s timed to perfection.