What is an “NHS crisis”? Lombardy-style scenes inside and outside our hospitals would certainly be one – with ambulances unable to move ailing people into A&E departments, desperate patients marooned on trolleys in corridors, and people left to die “in their beds alone at home, some of dehydration and starvation alongside their pneumonia, with no palliative care of any kind”, as Sam Bowman once put it.

Do a series of “critical incidents”, like those now declared in several hospital trusts, constitute a “crisis”?  No, some would say: the term doesn’t mean that any of them have stopped seeing emergency patients or are closing their doors, as Chris Hopson, the Chief Executive of NHS providers, has pointed out.

Yes, others would reply: if trusts believe that they “might not be able to provide range of critical / priority services [they need] to”, as Hopson puts it, and must create “a formal interim emergency governance structure to make prioritisation decisions at pace”, then there’s a crisis.

The uncomfortable truth for the Government is that there is no dictionary definition of an “NHS crisis”.  It isn’t verifiable in the way that a rise in interest rates, say, or a cut in a tax rate is – as a matter of fact.  Ministers are vulnerable to an “NHS crisis” existing as soon as the media declares one.

This helps to explain why the options facing Ministers when Covid first manifested itself were limited.  Vaccines didn’t exist. Drugs were fewer. Treatments were experimental, up to a point.  The choice was full lockdown, nothing, or partial restrictions, perhaps along Swedish lines.

It’s reasonable to believe that those days are gone – and that the main problem facing the Government, Covid-wise, is what to do in the period before enough people are properly vaccinated, against a background of higher immunity, better drugs, more treatments and mass testing.

Our recent survey of Conservative activists found a third in favour of vaccine passports during this interim, a quarter suppportive of the present measures, and a third against any restrictions at all, period.  There’s evidence that the long-standing scepticism of much of our panel about these is now held by the public more broadly.

A mix of choice and luck has got the Government into the same position.  The current restrictions are minimal, at least compared to the absolutism of the original lockdown and those that followed.  A hundred or so Tory backbenchers opposed even these.  The Cabinet came down against further restrictions pre-Christmas.

Boris Johnson was clearly under pressure from Government advisers to propose more restrictions, and seems to have been willing to consider them.  But everything we hear suggests that despite having nearly died of Covid himself, his instincts after his illness remained as before.

This, after all, is the man who told Dominic Cummings, according to the latter’s account, that “I’m going to get (Chief Medical Officer) Chris Whitty to inject me live on TV” with the virus.  And who with Rishi Sunak provided a different view in the Government’s original quad from the more prohibitive one of Matt Hancock and Michael Gove.

As I write, my media colleagues haven’t declared an “NHS crisis”: if and when they do, we will all know it.  There may be a war-weariness even among outlets willing to give more space and airtime to the zero Covid lobby.  But what is  doing most to shape the present political landscape, Covid-wise, is that Omicrom is less severe than Delta.

The question now is what happens as the former spreads from London to much of the rest of the country, with more severe restrictions in place in Scotland and Wales.  The prospect of hospital ICU beds being swamped is relatively unlikely, if the evidence from the capital so far is replicated elsewhere.

Thinking through the filter of a formula may help.  If the number of patients with Covid is A (whether or not it is the primary cause of illness) and staff absences are B, then the hospitals will cope.  There will be relatively few “critical incidents”.  Or harrowing footage on TV screens and social media.  The media won’t declare an “NHS crisis”.

But if the number of patients is C (C being higher in this case than A), or the number of staff absences is D (it being higher in this case than B), or both, then an “NHS crisis” there will duly be.  Or perhaps one will come later this month, as Omicron, Delta, flu, seasonal illness and bed-blocking take their collective toll.

At which point, Labour, which doesn’t want to get on the wrong side of public opinion by calling for new restrictions, (and didn’t raise Omicron from the front bench during Prime Minister’s Questions yesterday), will nonetheless call for them, and suggest that it has been doing so all along.

In such circumstances, any further restrictions might be not too little, too late but too much, too late – since Omicron would already be out there en masse, having spread wildfire-like through the population with relatively few people left for it to infect.

But if Johnson gets lucky, there will be no “NHS crisis”, and we will see if his and the Conservatives’ poll ratings then recover or not.  In the meantime, the balance of the argument favours cutting the Covid isolation period to five days, assuming that the relevant lateral flow tests return negative results. It has already been reduced from ten to seven.

The case against doing so is that that the test findings are sometimes wrong, but the Government is already discounting that factor in reverse – in other words, when the matter to hand is self-isolation after a positive result. The requirement for a confirmatory PCR test has been suspended.

A cut in the isolation period would raise the demand for lateral flow test kits of which there presently aren’t enough (though more people have been tested in the UK recently than in any other country).  However, under the circumstances this would be lesser of two evils, as dispensing with tests altogether would be the greater of them.

For it is appropriate to talk of an “NHS crisis”, it’s also right to talk of a “business crisis”, a “workforce crisis”, a “hospitality crisis”, a “rail crisis” – and much else, as Omicron absences take their toll on the economy.  The policy trick is finding a medium between spreading the virus unnecessarily and cooping people up unnecessarily.  For the moment, as hospital admissions and staff absences climb, Johnson will cross his fingers and pray for luck.