The verities of British politics – its stability, temperance and perceived permanence – are rapidly dissolving. Up to 70 per cent of those who voted Tory last May could be about to vote against the express wishes of the government, in the process forcing David Cameron to resign. If Britain remains in the European Union it will be largely thanks to Labour voters. Yet as many as 45 per cent of them could vote to leave tomorrow, and Brexit high command has been actively seeking their votes for months. Iain Duncan-Smith, who has said nothing about pay over the last six years, recently blamed stagnant wages on immigration. The most prominent Brexit arguments increasingly aren’t about competition or red tape, but protecting the NHS, improving access to council housing and increasing wages – even though leaving the EU wouldn’t help with any of those issues. Talk of ‘Red Ukip’ – a combination of social conservatism and anti-elite populism – came to nothing at the last general election, but it is now the default politics of the leave campaign.

Labour, historically, has been an alliance of the poor and people who care about the poor, but at the moment that alliance looks like a thing of the past. The party’s base is visibly splitting into two groups, which disagree on a range of issues, not least Europe. One group is younger, more racially diverse and the avant-garde of a liberal social agenda. The other is older, more socially conservative and more prone to view the failures of globalisation through the lens of immigration.

Ukip failed to win a single Labour seat in England’s east or north last May. But it came second in 120 constituencies, and could prove alluring in the next general election to the significant minority of Labour supporters likely to vote leave. For the likes of Rachel Reeves, Tom Watson and Tristram Hunt, the answer to that is to pivot right, undermining Ukip’s offer by approximating it. But not only is this offer not believed among Labour leave voters, it offends the other half of their base, the metropolitan left who form the core of the remain vote.

Whatever the result this week, in order to come anywhere near power Labour has to maintain its shakey alliance at all costs. That won’t be done by ‘having a conversation’ about migration or ‘listening to concerns’. Nor will it be achieved by dodging objections about low wages by claiming globalisation is an unalloyed good. Hunt and Watson can’t make a commitment to free markets without accepting the free movement of people. If they don’t want one, they can’t have the other.

So how might the Labour alliance be maintained? It isn’t enough for Corbyn to be opposed to austerity; he also needs to make a decisive break with the Blair-Brown years. He must admit that globalisation isn’t working for Britain’s poor, but the solution isn’t border controls. Labour could offer a properly enforced minimum wage of £12 an hour, a return to closed shop unions and a state that is far more active in industrial policy. The housing crisis needs be addressed through a combination of rent caps and increasing the supply of council housing. The implementation of this offer would be guaranteed by the end of a first Labour term. Critics will insist it is undeliverable, but the alternative is a breakdown in the coalition on which the party has historically depended, and without which it will never govern again.