There was much surprise when Theresa May named Boris Johnson Foreign Secretary on 13 July 2016 (not least from the man himself). But the appointment was hailed by some as a political masterstroke. By putting the Brexiteers in charge of Brexit, May, it was said, had followed the Pottery Barn rule: “you break it, you own it”. And in naming Johnson Foreign Secretary, she had shrewdly kept a leadership rival inside the tent.

Two years on, May’s decision, to put it mildly, has not aged well. Johnson has performed the rare act of pissing inside the tent as well as outside of it. He has routinely humiliated May at home and the United Kingdom abroad. Indeed, it sometimes feel as if he is writing a book entitled 100 ways to cheat the sack.

Johnson’s latest offence was to assert last month that British laboratory Porton Down was “absolutely categorical” (had “no doubt”) that the poison used in the Salisbury attack originated from Russia. In fact, as it transpired on Tuesday, UK scientists could not determine “the precise source”. Johnson’s typically loose lips gifted Russia its biggest political victory since the attack (the Foreign Office, to the Kremlin’s glee, was forced to delete an inaccurate tweet).

The surprise is that anyone should be surprised. Johnson is an accident permanently waiting to happen. This is the man who wrongly told the Foreign Affairs Select Committee that Nazanin Zaghari-Ratcliffe was in Iran to train journalists (the second anniversary of her imprisonment passed on Tuesday, with no prospect of release), who accused French president François Hollande of contemplating Nazi-style “punishment beatings”, who said the Libyan city of Sirte could be like Dubai once “the dead bodies” were cleared away, and who recited Rudyard Kipling’s colonial-era poem, “Mandalay”, in Myanmar (forcing the British ambassador to interject). Johnson is one of the world's foremost practitioners of anti-diplomacy.

His overweening ambition to become prime minister has led him to shamelessly flout collective responsibility. His 2017 Conservative leadership bid (disguised as a verbose Daily Telegraph article) disrupted the party’s conference and helped precipitate the speech that nearly killed Theresa May.

Again, the surprise is that anyone should be surprised. Dishonesty, ineptitude, truculence and narcissism are the hallmarks of a man who was sacked by the Times for fabricating a quote and by Conservative leader Michael Howard for lying about an affair. In defiance of the nation’s finest economist and statisticians, he has continued to promote the mendacious claim that the UK will gain £350m a week or more if it leaves the European Union (in fact, it is forecast to endure a net fiscal loss of nearly £300m a week).

In normal times, Johnson would have been sacked long ago. But these are not normal times. Theresa May, forever damned after blowing her party’s majority, cannot dismiss Johnson for fear of collateral damage.

And so Johnson (who journalists privilege by calling “Boris”) continues to hold sway at King Charles Street. An austerity-ravaged Foreign Office, once lauded as proof of British “superiority”, now merely exhibits its decline.