On New Year’s Day The Critic published my piece “Boris Johnson: a study in success?” in which I sketched the spectacular success of the PM’s political career so far, and speculated whether his luck would continue to hold or whether some unforeseen disaster would bring him crashing down in flames.

Now that we have reached Easter it is time to make an updated quarterly report. How is the year panning out for the prime minister? In the credit column there is one story, and one alone, that dwarfs the manifold failures of his government’s handling of the Covid-19 pandemic. That story is the astonishing success of Britain’s vaccination programme.

Thanks to Britain’s foresight in buying up in advance huge quantities of vaccines produced by the AstraZeneca, Pfizer-BioNTech and other companies, half the UK population — thirty million people — have already received an initial inoculation. As a result, infections, hospitalisations and deaths are in free fall and there really are cracks of light appearing at the end of the long dark Covid tunnel.

This seemingly miraculous success story comes in stark contrast to the embarrassing failure of our nearest European neighbours. France, Germany and Italy are grappling with a third wave of the pandemic, a bureaucratic nightmare in getting vaccines into the arms of their people, and a reluctance among significant numbers of those people to get vaccinated at all.

Boris’s reputation as a wildly philandering adulterer was widely known and has already been priced in

The smooth rolling out of Britain’s vaccines so far has resulted in a rumbling vaccine war with an EU already enraged by Brexit and now envious of the success of a neighbour they had written off with contemptuous scorn. But the success of Britain’s vaccination programme and the EU’s hysterical reaction to it has done Boris’s government no harm at all: in fact, it has delivered a bonus in the form of a stonking opinion poll lead over a lacklustre Labour opposition and has seemingly validated Brexit, even in the eyes of many former Remainers.

So far for Boris, so good. His fabled luck has held. But before any sense of smugness and complacency sets in, what is there in the debit column to set against the miraculous vaccine success? There are a number of ticking time bombs strewn along his primrose path, any one of which could go off with devastating effect for his personal popularity and his political survival as prime minister.

Let us take the latest one first: the confession in The Mirror by Jennifer Arcuri that she did indeed enjoy a steamy four-year affair with Boris when he was Mayor of London and still a married man. I think that this will prove the least of the PM’s worries. To put it plainly, Boris’s reputation as a wildly philandering adulterer was widely known and has already been priced in. Britain today is far more tolerant of sexual behaviour that, if known in past times, would have brought a speedy end to political careers.

The lack of a credible opposition has thus far saved Boris from the consequences of past errors

Besides, Boris is far from the first prime minister to have been an adulterer. The Duke of Wellington was such a well-known libertine that when the courtesan Harriette Wilson threatened the Iron Duke with an Arcuri-style exposé in her memoirs he famously told her to “Publish and be damned”. She duly did, and publication did Wellington’s political career no harm at all. Lord Palmerston was known as “Lord Cupid” for his erotic adventures. He is thought to have fathered seven illegitimate children, and when it was rumoured that he had sired another in his seventies Disraeli advised that the report should be suppressed lest he sweep the country in an election.

William Gladstone picked up prostitutes and took them back to Downing Street, allegedly to save them from a life of sin. H. H. Asquith was notoriously “unsafe in taxis” and spent Cabinet meetings during the First World War scribbling love letters to his paramour Venetia Stanley. His successor Lloyd George was nicknamed “the Goat” for his philandering and made his mistress Frances Stevenson his principal political secretary — the first woman to hold such a position.

So, if such precedents make Boris safe from sexual scandal, is he vulnerable on any other front? Much more potentially damaging is the allegation — now subject to an inquiry — that as Mayor of London he authorised the payment to Arcuri’s firm of £126,000 in public funds during their liaison. A public accustomed and inured to stories of Boris’s lively love life may be less indulgent if he is proved to have misused their money.

Similarly, there are growing demands for a full public inquiry into the government’s handling of the pandemic, particularly the awarding of PPE contracts to companies with connections to the Conservative Party. The government has shown no great enthusiasm for setting up such an inquiry and, until they do so, any whiff of corruption surrounding such claims will only continue to grow stronger.

Then there are the effects of Brexit on the economy. If the excessive paperwork and bureaucracy affecting UK exports to the EU prove to be temporary teething troubles or can be blamed on the pandemic, well and good. But if they result in businesses going bust and a consequent substantial loss in jobs, then there will be trouble ahead.

Finally, we are not out of the Covid woods yet. If new variants of the disease cause more lockdowns and dissipate the vaccine bonus, it is likely that growing public impatience with lockdown restrictions will snap and spill onto the streets resulting in more unrest such as the recent disorders seen in Bristol. A long hot summer of discontent may await.

The scientific miracle of vaccination and the lack of a credible opposition has thus far saved Boris from the consequences of past errors and carelessness. But any one of the “events, dear boy” that blow governments off course and run the ship of state aground could yet blow up in his face. His fate and ours hangs on the point of a needle.