So, although more than 17 million people voted for parties that wanted a second referendum compared with fewer than 15 million who did not, on 31 January Britain will leave the EU on Boris Johnson’s terrible deal. What he presents as an irrefutable, unarguable validation of Brexit is in truth a democratic travesty. When Brexit goes wrong, as it will, there will be a reckoning – if a sufficiently viable opposition exists to force it.

Tactical voting had some successes, but so precipitate was the drop in the Labour vote and so resilient the Tory one that it was overwhelmed. Looking back, it is obvious that the Labour party should have joined the Remain alliance to avoid splitting the Remain vote, and its point-blank refusal to do so should not have been accepted so tamely.

The country would have been voting for what it needs: staying in the EU at a perilous moment in world trade in order to secure vital economic growth, while launching a wholesale programme of national reconstruction and the resetting of its broken capitalism. The Tory party – not the Labour party – would be facing questions over its purpose and future.

But even to write this paragraph is to recognise its impossibility. Simple majoritarianism is embedded in our political culture, and it was never going to be challenged by Jeremy Corbyn, in this context a supreme conservative, and a significant part of the Labour party. Instead, the mission on 12 December was to seek a mandate in a winner-take-all system for their radical socialist manifesto. The building of a broad coalition in today’s very particular circumstances, along with the overt political compromises, was not the political project. It was anathema, particularly to the sect that had won control of the Labour party.

The paradox is that, had the party had an electable would-be prime minister it would not have needed the Remain alliance. The double paradox is that had Corbyn been part of it and thus potential leader of even a putative interim government, its vote share would have nosedived. Our country may be quietly liberal, tolerant and good-natured – but it is also quietly and deeply patriotic. For too many, particularly in the working class, a vote for an apologist for the IRA and Hamas, an indulger of antisemitism and a convinced pacifist was an unpatriotic, anti-British act – however much they might sympathise with the direction of economic and social policy.

‘Corbyn would have been at home as a conscientious objector. You can respect that position. But a majority of the British will never elect such a man their prime minister.’ Photograph: Toby Melville/Reuters

Johnson might be a narcissist, a twister, a liar and a toff – but in his witty one-liners and breezy optimism they recognised him, however rogue and untrustworthy, as a member of the English officer class, on the battlefield, at least. Corbyn, in contrast, would have been at home as a conscientious objector. You can respect that position. But a majority of the British will never elect such a man their prime minister.

A more surefooted Labour movement would have recognised this brutal truth from the beginning. Time was when the leadership of the trade unions, genuinely in touch with popular values, would have simply vetoed Corbyn’s candidature – or seen their error and dispatched him and his coterie. In this respect, Len McCluskey and the group at the top of Unite who backed Corbyn so uncompromisingly are also part of the crisis now engulfing Labour.

They did so because they believed he would lead them to the promised socialist land – of which the 2019 manifesto was the quintessential expression, although on Friday McCluskey said it contained an “incontinent rush of policies”. I do not doubt Corbyn’s decency and his devotion to peace. But if you want to win a British general election with our toxic rightwing press, the precondition is a plausible leader and a feasible programme of government. Corbyn and Corbynism were neither. The danger now is that his followers will take no responsibility for what happened, lionise him as a martyred messiah and turn the 2019 manifesto into an unchallengeable icon. It is no such thing. It is true that no member of the liberal left can seriously challenge its laudable ends – a much more equal society, a transformation of our economic base to meet the environmental emergency and radically improved public services based on inclusion and universalism. But the trouble was the means. This was an indiscriminate, fantastically expensive statist push on all fronts – alongside some measures, like wholesale semi-confiscatory nationalisation, unnecessary to achieve the stated ends. There was no recognition that a vibrant, purpose-driven private sector is an indispensable part of any economic structure – and no attempt was offered to conjure it into being. Instead, the state and its agencies were to become Britain’s economic drivers. It stretched credibility to the limits.

All this can and must be recast, especially as Johnson attempts to develop a wholly unthought-through “one-nation” prospectus, while preserving the powerful nexus of private equity and hedge fund operators who prey so destructively on British business and finance. They are his funders. Labour – and the Lib Dems who once again mistakenly retreated from a substantive critique of Britain’s capitalist structures – must have a credible alternative.

Nor must the Corbyn clique be allowed to blame Brexit for the cataclysm. There are two million more Remainers than Leavers, the Tories own the Leave vote and Brexit is about to become deeply unpopular as it becomes clear that Johnson’s promises lead to the hardest of Brexits, with the spate of plant closures and disinvestment accelerating. Nor is there a majority in the country for a one-sided trade deal with the US. The right position in both principle and practice is to remain pro-EU, even though the country may be hyper-weary of the Brexit deadlock.

Equally, Labour must be constitutionally creative. The Corbynite proposition that all Scotland wanted was Corbyn-style socialism was total nonsense. Only a full-blooded new federal deal has the remotest chance of saving the union – and enfranchising left-behind England.

Is any of this possible? It may be that the McCluskey, Momentum and Corbynite hold on Labour is impossible to challenge. In which case it will be broken as an electoral force. Parties do not have God-given rights to prosper. Nor do countries. Britain, like declining civilisations before it, could be locked in an irresistible downward vortex. Unless a viable Labour party can be created fast, Britain is entering the same pit.

• Will Hutton is an Observer columnist