MPs kept wishing each other a merry Christmas, but this was about as unmerry a PMQs as could be imagined. It lasted, as is now customary, for 50 instead of 30 minutes, and long before the end, it seemed unlikely that anyone would say anything witty enough to discomfort Theresa May.

More time is good, in the sense that it enables plenty of backbenchers to be called. But it is bad when it becomes an incentive to be dull and diffuse.

PMQs at its best can be like the most brilliant tabloid journalism, which casts sudden, penetrating flashes of light on difficult subjects, by cutting through the surrounding thickets of verbiage and obfuscation. But with May and Corbyn as the principal performers, that happy outcome is improbable.

The Prime Minister looked more confident than at any time since the general election. She believes she has seen off her enemies, and that in the war of attrition between herself and Jeremy Corbyn, she has gained the upper hand.

But wars of attrition are far from wonderful for the spectators, and this one certainly won’t be over by Christmas. Rather unkindly, she reminded Corbyn of his foolish prediction that he would be Prime Minister by Christmas.

At this rate we could see no war of movement breaking out for the next four years. The exchanges were so sterile it was hard to avoid falling asleep.

May behaved rather as she did when Home Secretary. After much thought, she has decided where to dig in, and nothing is going to shift her. There is a sort of self-satisfied impregnability about her. Her opponents feel she ought to be easy to defeat, but somehow she isn’t.

She dismissed the claim by Rosena Allin-Khan (Lab, Tooting) that in Wandsworth, 2,500 children will wake up homeless on Christmas Day. With righteous indignation, the Prime Minister pointed out that this made it sound as if 2,500 children would be sleeping in our streets, which is not the case. Accommodation is provided for all families with children.

She then took aim at Corbyn, who wanted her to promise that the NHS will get all the resources it needs, and will meet all its targets. May saw him off by pointing out that someone once described Labour’s NHS legacy “as a mess” – Corbyn himself!

The Leader of the Opposition was quite incapable of thinking on the spur of the moment of a wounding riposte to this thrust. He ploughed on with his prepared questions, and will comfort himself that he provided a soundbite for the television news.

But in parliamentary terms, he had been trampled upon, and will have no chance to reverse that setback until the second week in January.