Maybe Jeremy Corbyn thinks a “coup de grace” is an exotic ice cream, which true socialists should not administer.

The Government is reeling from its defeats last night on Brexit, one of which, on the contempt motion, was inflicted by his colleague Sir Keir Starmer.

Does the Leader of the Opposition seek to follow up these successes by harrying the discombobulated Prime Minister? Does he recognise that this is an extraordinary week, when her parliamentary weakness has been exposed in the most humiliating way?

Does he ridicule her in front of her own backbenchers, and make them embarrassed to support her? Does he seek to avert the danger that she could yet turn her weaknesses into a strength?

Of course not. Corbyn loyally avoids the whole subject. He offers her a rest from Brexit, a chance to regain her composure. It is hard not to conclude that he is trying to prop the Prime Minister up.

Attacks on her could, of course, misfire, and prompt her own troops to rally round and defend her. But Corbyn’s duty is to find some way of demonstrating that she has become indefensible.

Instead he talked about Universal Credit. That is a worthy subject, but also, just now, a culpable evasion of the great issues which confront not just the Conservative Party but the nation.

As a result of Corbyn’s dereliction of duty, Prime Minister’s Questions was a complete anti-climax. Corbyn paraded his virtuous concern about poverty, and various other MPs paraded their virtuous concern about various other issues.

Politics in these circumstances becomes a barren series of postures. The House was boisterous, but Corbyn gave it nothing to be boisterous about.

Ian Blackford, for the Scottish Nationalists, suggested “the Prime Minister has been misleading the House inadvertently or otherwise”, was ordered by the Speaker to rephrase this in order to avoid any  “imputation of dishonour”, and did not really get any further.

But Blackford is only allowed two questions, and is not auditioning to be the next Prime Minister.

Perhaps Corbyn, who each week manages to waste six questions, fears May might be replaced by someone who shows him up as  a third-rate parliamentarian.