If sanctimony could kill, Boris Johnson would have expired yesterday afternoon, the first time his fixed penalty notice was discussed in the Commons by Sir Keir Starmer.

But to the indignation of the Leader of the Opposition, the Prime Minister survived that ordeal.

This left Sir Keir with a choice. Having climbed up on his high horse, should he continue in the same sanctimonious vein, or might it be better to rest the subject of the Downing Street parties, which is bound before long to return, and to ask the PM about something else?

Sir Keir opted for more sanctimony. Perhaps he thought that on Tuesday he had failed to administer a lethal dose, and that by radiating sanctimony across the Despatch Box for a second day running, he could finish Johnson off.

But sanctimony can be dangerous also to whoever radiates it. The more one claims to be holier than thou, the less attractive one may sound, and the fewer friends one may find one has.

So Sir Keir decided to make some friends. It was reported that Johnson, when addressing Tory MPs last night, had criticised the Archbishop of Canterbury and the BBC for attacking the Government’s Rwanda migrants plan more vociferously than they had attacked Vladimir Putin.

Sir Keir today called on Johnson to “apologise for slandering the Archbishop”, and went on to accuse him of attacking the brave BBC journalists who have been reporting from Ukraine.

Johnson bridled: “I said nothing of the kind.” Yesterday he made a great show of contrition. Today it was equally important that he demonstrate fighting spirit. Otherwise people would think his spirit had been broken.

This accusation that he had been “traducing journalists” showed, the Prime Minister declared, that Sir Keir “must be out of his tiny mind”.

Johnson also found occasion to call Sir Keir “a Corbynista in a smart Islington suit”. After all, had not Sir Keir campaigned at the last general election to have Jeremy Corbyn made Prime Minister?

Politics is often a matter of choosing the lesser of two evils: a point which sanctimonious politicians refuse to admit.