“Where have you been all this time” asked most of Yorkshire.

“Haven’t you heard?” Boris Johnson replied. “There’ve been terrible floods. Why on earth would anyone want to come here now?”

“But you’re the prime minister.”

“I know. And I’ve just come up with this absolutely cracking wanking gag.”

“We need help. Hundreds of us have lost our homes. A woman has died.”

“Seriously, you really do need to hear this wanking gag.”

On the way down to the London Electric Vehicle Company, in Coventry, Johnson’s advisers had second thoughts. The Yorkshire visit had been a PR disaster and joking about onanism probably wasn’t such a great look after all. Apart from drawing unwanted attention to the fact he couldn’t be entirely certain of just how many children he did have, it would also highlight the fact that Johnson’s entire political career had been based on pleasuring himself. A succession of petites morts for Boris. One long grande mort for the country.

There’s been a very good reason why Johnson has kept a low profile so far in this election campaign. He is not the great communicator and leader he has built himself up to be. Having been deprived of his masturbation punchline Boris appeared to sulk through most of his speech to a largely indifferent audience of factory workers. Most of his other jokes failed to land and his ad libs became ever more staccato and random as he desperately tried to jolly everyone along.

He really only knows he’s alive if he gets a few laughs and when none come, he becomes a shrivelled, needy homunculus. Not that this could really be classified as a speech. Rather a collection of assorted thoughts and lies that had been strung together at the last moment. He began by bizarrely comparing the UK economy over the past nine years to a racehorse with three legs. Boris didn’t appear to know that horses in this condition can get shot on the spot.

Johnson then moved on to his familiar Brexit lies. Parliament had blocked Brexit for the past three years. He still hasn’t quite realised that no one has done more to block Brexit than himself – first by leaving Theresa May’s government and voting against her deal, then by pulling his deal and demanding an election after his withdrawal agreement had won a comfortable majority in the Commons. At times like this the prime minister is the sociopath’s sociopath. So detached from any objective reality, truth and lies have become interchangeable.

The metaphors came and went, each one dying harder than the last. He had an oven-ready deal. One that Theresa May had rejected and which he himself had said no UK prime minister could endorse. It was the Pot Noodle deal. Just add water. So it should go down well in Yorkshire then. They’ve got plenty of water there right now. It’s hard to imagine a less sensitive prime minister. A straw man with a tin ear. He mumbled on. Actually it was a Blue Peter deal. One he had made earlier. Great. Almost everything made out of two toilet rolls and sticky-back plastic fell apart after 20 minutes. On reflection, that might have been one of the truer things he said all afternoon.

Still the lies tumbled out. Jeremy Corbyn was committed to two referendums in a year even though he had said the exact opposite. Labour was going to spend £1.2tn on a manifesto that the Tories had written for them. He was going to build 40 hospitals. Out of Lego. The country was on the verge of a green revolution. The future was bright. Shame, then, that there had been a power cut only that afternoon as Tesla had said it was no longer going to build its gigafactory in the UK due to Brexit uncertainties.

“Er … that’s about it,” he said. Though he could just have easily have wound things up 20 minutes previously, as he had clearly come with nothing to say other than the wanking gag, which the girly swots around him had insisted wasn’t statesmanlike. Hell, he’d never pretended to be that. He was just a chancer who had got lucky and, when asked, couldn’t even remember where the floods had taken place. “Stainforth,” he blurted eventually. “And … elsewhere.” The people of Yorkshire must feel so cared for.

During the Q&A one Sun journalist wanted to know what had happened to the wanking gag. Boris’s pasty face flushed pink and he blustered. He couldn’t imagine what had happened to the joke he had written. A complete mystery. There would be a full public inquiry. No need really. The gag had just been buried in the sub-text. The whole speech had just been casually tossed off. And no one but him had derived any pleasure from it. All he had to show for it was a lingering sense of shame.

John Crace’s new book, Decline and Fail: Read in Case of Political Apocalypse, is published by Guardian Faber. To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min. p&p of £1.99.