Michael Meacher has never had a sense of humour. He showed that when he fought and lost a ridiculous libel action against the late Alan Watkins, and he showed it again today at Prime Minister’s Questions when he bridled at David Cameron’s suggestion that he, Meacher, might have taken “mind-altering substances”.

Labour affected, and perhaps even felt, great outrage at this remark. It prompted Ed Miliband to adopt his most moralistic expression: he mouthed or perhaps even spoke the words “you can’t say that”, and gazed with passionate entreaty at the Speaker, John Bercow, urging him to rebuke Cameron for saying such hurtful and unjustified words.

But Meacher is the last man one would suspect of taking any kind of illegal drug. It would be surprising if he takes anything stronger than a cup of tea. His demeanour is that of sober, strait-laced socialist who has come straight from a round-table discussion with Beatrice and Sidney Webb about the runaway success of central planning in Soviet Russia.

Bercow permitted Meacher to make a point of order. Meacher proceeded to ask whether it was in order to use “such an unjustifiable, rude and offensive phrase”. Cameron responded with a smile that he had “made a light-hearted remark”, that if he had caused offence he of course withdrew it, but that he thought it important for the Commons to be able to have “a little bit of light-hearted banter”.

So Cameron ended the day as the man with the sense of humour, which is a considerable though not always decisive advantage in public life. His own backbenchers enjoyed his performance more than they have for some time. The distressing revelations in recent days about the private life of the Reverend Paul Flowers, former head of the Co-operative Bank, had given Cameron plenty of material to work with.

Miliband tried to score by accusing Cameron of closing children’s centres. Cameron wisely admitted that one per cent of the 3,000 centres have closed. As so often, Miliband began well, with short and pointed questions, but had somehow run of steam by the end.

Cameron most unsportingly quoted a dismissive tweet about Miliband’s performance by Tony McNulty, a former Labour MP and minister, who said the public are desperate to find  “a Prime Minister in waiting”, not “a Leader of the Opposition indulging in partisan Westminster village knockabout”. McNulty’s hopes of getting back into the Commons have just taken a fatal hit.

But it is not good for Miliband to find his thunder stolen by such minor figures on his own side as the earnest Meacher or the considerably less earnest McNulty.

Cameron today demonstrated that he can do partisan Westminster knockabout as well as anyone. But he also ignored two or three opportunities to give his verdict on the remarkable speech delivered yesterday by Nick Boles, one of the Conservative Party’s best known modernisers.

The Prime Minister did not have to follow Boles’s call to “shout from the rooftops” about liberal policies including gay marriage. But this was a chance for Cameron to strike for a moment a more serious note, and give an indication of the direction in which he is trying to take his country and his party. To this column’s regret, the Prime Minister decided to remain at the knockabout level.