Twenty minutes before Prime Minister's Questions, the government presented Jeremy Corbyn with a gift: the biggest Budget U-turn in recent history. Having defended the National Insurance increase only days ago, Theresa May humiliatingly abandoned it. Here appeared a target that even Corbyn could not miss.

But to the incredulity of Labour MPs, he did. Corbyn failed to produce a single memorable line and failed to ask any of the essential questions (indeed, sometimes he didn't ask questions at all). After correctly surmising that the government appeared to be "in a bit of chaos", Corbyn bizarrely segued into an attack on bogus self-employment (which May has handily established a review to examine).

The Prime Minister ruthlessly replied: "I normally stand at this despatch box and say I won't take any lectures from the Hon. Gentleman. When it comes to lectures on chaos, he'd be the first person I turn to." From that moment, the grimaces on the faces of Tory MPs were replaced by those of Labour MPs. Corbyn correctly asked how the government would fill the black hole left by the U-turn but overlooked far more potent questions: when did Theresa May first learn of the tax rise? Did she know it breached a Tory manifesto commitment? Did the Chancellor offer his resignation?

By Corbyn's third question, any pressure felt by May had entirely evaporated. To the Tories' delight and disbelief, the Labour leader was more interested in condemning bad businesses than a bad government. Corbyn's fourth question wasn't one at all: “We have a government U-turn, we have no apology and a Budget that falls most heavily on those with the least broad shoulders ... That is the agenda of her government and everybody knows it.” May gleefully replied: "I don't think the Right Honourable Gentleman's quite got the hang of this, he's supposed to ask a question when he stands up."

By the end, unwilling or unable to probe the biggest U-turn of May's premiership, Corbyn had switched subjects to grammar schools. Labour MPs looked both outraged and dumbfounded by Corbyn's masterclass in anti-opposition.

It was left to others to show the Labour leader how it's done. Angus Robertson assailed May's "screeching, embarrassing U-turn" (prompting a fierce glare from the PM). Yvette Cooper, Corbyn's former Labour leadership opponent, expertly noted: “The PM’s just done a £2bn budget U-turn in the space of a week; last year the government did a £4bn U-turn in the space of five days. Is that why they want to abolish spring Budgets? Because they just keep ripping them up?”

More perhaps than any other occasion, today's PMQs was proof that Corbyn is leader of the opposition in name only.