Sir Keir Starmer arrived in the Commons with a spade, dug a deep hole, placed some sharpened stakes at the bottom of it, and proceeded to invite Boris Johnson to impale himself on them.

There have, Sir Keir remarked, been “people saying the Covid statistics appear to have been manipulated, that Monday’s roadmap is based on dodgy assumptions and false modelling”.

He urged the Prime Minister to agree that such comments were “irresponsible”.

Were Johnson blind, he might have fallen into this trap, but since his eyes work well enough, he walked round the hole which had been dug for him, remarking as he did so that the roadmap has set us “on a cautious but irreversible journey to freedom”, and the data on which it is based were presented on Monday to the House.

Sir Keir now revealed that “all these comments came from his own MPs”. He had been trying to trick Johnson into condemning “the 60 or so members of the Covid Recovery Group”.

One cannot blame the Labour leader for attempting to exploit this division within the Conservative Party, but one has to say that his attempt to do so lacked subtlety.

Johnson was in boisterous mood. He dismissed Starmer’s demands for next week’s Budget as “paltry”, mocked him for weaving “hither and yon like some druidical rocking stone”, and concluded: “He vacillates, Mr Speaker. We vaccinate.”

Nor did anyone else manage to discomfort the PM. It was notable that when replying to Ian Blackford, Commons leader of the Scottish National Party, Johnson did not seek to capitalise on the Nats’ ferocious internal disputes in Edinburgh, but instead concluded: “All they want to do is break up Britain with another referendum.”

It is not good for the Commons for the Prime Minister to win such easy victories. It may not even be good for the PM, who at this rate may become over-confident, and tumble into some trap of his own making.

Johnson holds the initiative. When one considers how tough the last year has been, that is quite an achievement.