Armageddon awaits. Boris Johnson is heading for No 10 and there is nothing dishonest, disreputable or even scandalous enough that he can do to stop his party choosing him now. They know of his lies, laziness and narcissism, but they don’t care. After a crushing humiliation at the polls in Thursday’s EU election, where the Tory vote may fall to single figures, this drowning party will clutch for the straw-headed showman to save them from triumphant Faragists. Well, Prime Minister Johnson would provide a fitting finale to this ever-darkening decade.

A measure of the demented state of the Conservatives is the number of hats in the ring for this most poisonously impossible job. Who would want to lead a paralysed government with no majority and a party that is a nest of vipers? Anyone applying should be disqualified on grounds of diminished responsibility.

Who would want to lead a paralysed government with no majority and a party that is a nest of vipers?

The ultras have sworn to hold candidates’ feet to the fire, binding them to vote against Theresa May’s deal and for no deal. As Dominic Raab tries to out-Brexit Johnson, watch the two vie to make the most extreme pledges. The party will opt for a no-dealer because that’s what the grassroots want. They think only a no-deal stand can stop Nigel Farage’s tanks rampaging on to Tory constituency lawns. They’re wrong, because whatever Brexit they deliver, nothing will stop Farage claiming a “betrayal by the elites”. It’s a revolutionary cry of shatteringly effective simplicity. The Tories need to understand (and so do Labour) that no Brexit can ever be absolute enough; even the hardest no deal still needs endless arrangements to be made with the EU, which Farage can present as betrayals. It’s time to call out the myth of the “clean break”, when no deal still means interminable Brexit drama. Johnson won’t do that because he is cut from the same dishonest cloth, exploiting the same simplistic “get it over with” fallacy.

Surely, say people yearning for reassurance, wiser Tory MPs will prevent Johnson’s name reaching the last two for the party to select? No, that would take exceptional bravery, and there are only a handful of principled moderates left: three of the best skipped off to Change UK just when they were most needed in their former home. Nicky Morgan, launching a “declaration of values” this weekend, said the moderate One Nation caucus would “work to stop any leadership candidate who endorses a ‘Nigel Farage No-Deal Brexit’”. Good, but she can only muster 60 MPs to block Johnson, while he has powerful backers: “It would be monstrous if Tory MPs deny Johnson his shot at Downing Street,” threatened the Mail on Sunday. Grassroots constituency chairs have fists at the ready and sleeves rolled if MPs fail to put their favourite on the ballot paper.

Johnson will rely on a party traumatised by this week’s results. He woos MPs one by one, claiming only he can save their seats. He uses his Telegraph column for crude grassroots rabble-rousing, on Sunday attacking “cock-eyed crook-coddling”, with criminals “cosseted in spas” and “murderers let out to murder again”.

What happens when he wins? He can’t get no deal through this parliament, but at Halloween the UK is due to crash out willy-nilly, without some deal agreed. The Calais border would clang shut and so would the Irish border, firing up demands for a united Ireland referendum, with the Scots likely to follow suit with Indyref2. As everything seizes up, Britain would have only the feckless Johnson to cope with a pile-up of calamities in fuel, food, medicines, visas, lorry queues and a plunging pound.

Johnson has no plan: his foresight goes no further than winning the prize of Downing Street. If he had the impulse control to visualise consequences, would he want to win on a no-deal pledge? Before 31 October, Labour would table a vote of no confidence and Tory One Nation MPs would back it to bring down their own government, and call an election. Seeing that inevitability, Johnson will surely call an election himself, shortly after reaching No 10. At risk of becoming the shortest serving prime minister of all time, he will be tanked up with vaunting hubris. Farage will bid to strip off Tory votes and seats (and some Labour ones too), while the Liberal Democrats syphon away remain and moderate voters. In the best scenario, the Armageddon that awaits may turn out to be the fate of Johnson and the Tory party for years to come, but not of the country as a whole.

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But never imagine that a Labour general election victory can be guaranteed. Take heed of the bitter Australian election result, so painfully familiar to the left here. From every doorstep the (very few) canvassers report a mass flight of Labour voters to remain parties. Jeremy Corbyn’s bad-tempered Andrew Marr Show appearance on Sunday failed to stem this Brexodus. Only the desperate detected any shift in his empty mantras on a confirmatory vote, as he wasted a last chance to save Labour votes.

Expect an almighty row about an entirely avoidable setback when Labour’s bad results come in. Will the lesson be learned that facing both ways fails? With a general election likely, Labour cannot fight Johnson and Farage with a miserable semi-Brexit offer of renegotiation plus confirmatory vote. In that confirmatory vote we need to know that Labour would unswervingly back remain. If not, the five remain parties could take enough slabs off Labour to deny it victory. After a decade of Tory devastation, every sane person wants Brexit “done with”, but only a remain vote stops it dead. Even in victory, Corbyn risks becoming yet another flailing Brexit prime minister, leading a country doomed to never-ending Brexit hell. The Tories will slaughter themselves by electing Johnson. But Labour can only beat him by confronting all the lies he has told all his life about Europe.

• Polly Toynbee is a Guardian columnist