He could have riffed on George Osborne’s weak spots. It’s not as if he wasn’t spoiled for choice. He could have pointed out the autumn statement was predicated on the Office for Budget Responsibility finding £25bn of extra tax revenues down the back of the sofa in the four months since the last budget: money that could just as easily disappear back into the sofa in the next four months. He could have observed that the chancellor had just made affordable housing only slightly less unaffordable. He could have wondered why the Tory bar was now so low that George had got the biggest cheer for doing nothing by not cutting police funding.

He could certainly have made capital from Osborne screwing up working tax credits so badly in his previous budget that he had been forced to come back to the Commons for a resit. He could have even gone into profit by noting that the chancellor had made himself look a halfwit by falling into his own welfare cap elephant trap. But the shadow chancellor doesn’t do capital or profit. He does dialectics. Apocalypse Mao.

Replying to a budget speech that you haven’t seen is one of the more thankless tasks, and the faces on the Labour benches were looking increasingly grim as John McDonnell bumbled, fumbled and stumbled his way through his first effort. But John didn’t care, because John knew he had his own very special rabbit up his sleeve. His eyes sparkled as the moment when he would unite his party and sweep the Tories away came nearer. “Timing, John, timing,” he told himself, his hand foraged inside his jacket pocket. Out came a well-thumbed copy of Mao Zedong’s Little Red Book.

“We learn to do economic work from all who know how, no matter who they are,” he said beatifically. “We must esteem them as teachers, learning from them respectfully and conscientiously, but we must not pretend to know what we do not know.” Having made his point, he threw the Little Red Book across the dispatch box towards the chancellor.

John could already hear the Labour MPs behind him rise to their feet, cheering, as the Tories raised their white handkerchiefs in surrender while voluntarily asking to be sent to the pig farms for re-education. Let three hundred and thirty flowers bloom. The long march was over and his time had come. They think it’s all over ... It is Mao.

It only gradually dawned on John that it was the government benches who were doing all the shouting and laughing. Behind him, only the sound of one door slamming. The blood drained from the faces of dozens of Labour MPs, who had been looking to the chancellor’s statement for a glimmer of light after weeks of being wrongfooted on security. Some upped and left. Shots rang out from the Commons chamber. Better to self-purge than to be purged.

John was bewildered. When he’d tried out that gag the night before at the secretariat of his local politburo, everyone had fallen about laughing. “The Commons will love it,” Chairman Jez Cor-Bao had said. “No one will imagine for a minute that this will merely confirm many people’s view that the Labour party has been taken over by a load of old commies who admire a man now remembered mainly in the west for killing 45 million of his own people during the great leap forward. Why not go the whole hog and quote from Marx and Lenin, too?”

Tumbleweed began to roll through the Labour benches as false consciousness won the day. Osborne could scarcely believe his luck. What promised to be a day of utter humiliation had turned into yet another day of glory. He was officially again a genius who had rescued himself from his last bout of genius. At least until someone got round to marking his resit. But for now, he was going to enjoy himself. “Look,” he exclaimed gleefully, “it’s a signed copy”. Whether or not it was didn’t matter. The Tory backbenchers could no longer hold back a collective tidal wave of simultaneous orgasms. Take us. Take us nao.

George skipped and dodged his way through the pools of moisture that were collecting on the floor of the house as he made his way out. Sensing the mood, Jeremy Hunt decided that now was as good a time as any to bury bad news and agreed to talks with Acas. David Cameron even wondered if it was time to come clean and say it hadn’t been a pig. It had been a sao. And all McDonnell had been left with was its ear.