Donald Macintyre's Sketch: PM on a roll after escaping Miliband's VAT trap

David Cameron during Wednesday afternoon's PMQs (BBC)

The fox was not so much shot, as vaporised, atomised, pulverised, the molecular vestiges of what had nanoseconds earlier been its fur, teeth and ears sent careening into the upper atmosphere.

Cameron gave a broad smile and a wink to his wife and two older children when he saw them sitting in the peers’ gallery at the beginning of PMQs. But even though he is known as a blood-sports enthusiast, you wondered whether this was really suitable entertainment for the under-12s, watching their father, trained quadruped killer, in the flesh like this. More worryingly still, his daughter Nancy, in particular, seemed to revel in the gory spectacle.

The fox in question, of course, was the refusal by Cameron and Osborne to rule out the increase in VAT to which Conservative governments, including this one, have traditionally been addicted. Until yesterday, that is, and what had seemed like it was going to be an all too routine exchange. After the inevitable reference to Cameron announcing his “retirement plans” and his explanation that he had given a “straight answer to a straight question” Miliband was admirably succinct: “So here is a straight question: will he now rule out a rise in VAT?” MPs steadied themselves for the usual “There you are Mr Speaker. There are some straight answers he cannot give. Let’s give him another chance. Yes or no?” etc etc.

Except that Cameron then said: “The answer is yes.” Few audiences since spectators gasped at Harry Houdini’s escapes from straitjackets while hanging upside down from high roofs can have been thrilled as the Tory backbenchers.

To say that Miliband – and indeed Ed Balls – were nonplussed would be an understatement bordering on the criminal. Prepared they weren’t. “No one is going to believe him,” the Labour leader said when he had finally steadied himself. “No one is going to believe him.” This may be true but as a riposte it served mainly to underline how sensational Cameron’s answer had been.

After this, of course, Cameron was on a roll, forgiven for what would have been at other times have been an embarrassing error – thinking that Labour’s Michael Connarty was standing down at the election because that’s what it said in his brief – not to mention some metaphor-scrambling excruciating even by his own standards: “I will tell the Honourable Gentleman what is a lame duck – trying to get into Downing Street on the back of Alex Salmond’s coat-tails.” (A duck that then turned into a “poodle”.)

And he saved to last a Miliband-fratricide joke, laboured, but calculated to warm Lynton Crosby’s heart: remembering Richard III as “someone did in one of their relatives to get the top job and the country ended up in chaos”.

It may be of course, that Samantha Cameron and her two children were watching their man’s last Commons stand as Prime Minister, possibly even as party leader. But if so it was quite a way to go.