A hint of mortality, a memento mori for Boris Johnson. As soon as Prime Minister’s Questions were over, the former Chancellor of the Exchequer, Sajid Javid, rose to make his resignation statement.

One day, Johnson’s downfall may be precipitated when he is condemned by a once close colleague who has lost all patience with him, just as Sir Geoffrey Howe lost all patience with Margaret Thatcher and precipitated her downfall in 1990.

Javid did not seek to emulate Howe. His tone was rueful, at times humorous, rather than vengeful, at times lethal.

The House heard him in silence, wondering if it was about to witness an assassination attempt, but started to relax when Javid said he “did not intend to dwell” on the “Cummings and goings” of his resignation.

Johnson took the chance to grin broadly at that comic reference to his adviser, Dominic Cummings. Like many an awkward passage in English life, it was going to be possible to pass the whole thing off as a joke.

And yet there were moments when Javid spoke with deep feeling. “I’m a low-tax Conservative,” he said, and the Treasury “is the only tax-cutting ministry”.

The fiscal rules actually matter, and his successor, Rishi Sunak, must be “given the space to do his job without fear and favour”.

Another way of putting this would be to say that Johnson has got to treat his colleagues properly, or they will at length defenestrate him.

Johnson responded with a bogus Point of Order in which he heaped praise on Javid, saying how many “friends and admirers” the former Chancellor has.

The affair passed off harmlessly enough, but also amounted to a warning.

Jeremy Corbyn had earlier been somewhat better than usual, as he twitted Johnson for “skulking in his grace and favour mansion” rather than visiting the victims of the floods.

If Johnson himself was too busy, Corbyn remarked, perhaps he could send Cummings to visit them. We found ourselves with “a part-time Prime Minister”.

Johnson looked riled by this, and retorted that the “hottest topic” on the Opposition benches – which it should be mentioned were by no means full – was what job Corbyn should get in the next shadow Cabinet, with Labour consumed by “narcissistic debate” about its own future.

The Prime Minister remains in ebullient spirits, but in ten years’ time it may well be the Conservatives who are consumed by narcissistic debate about their own future.