Sometimes in politics it is necessary to believe something before you know it is true. For the past decade, the radical left’s insistence that the liberal centre was facing imminent collapse was such a belief. It felt at times like a fantasy concocted by ideologues, student radicals and old-fashioned socialists, as indeed we were. For those of us active in the labour movement, the related argument that bold, radical ideas are more electable than endless pandering and triangulation is not just correct – it is a necessary belief for something like Corbynism to exist.

Maybe, some of us secretly thought, the centre would hold. Maybe the conservative technocrats would find a way out and centrist social democracy would reformulate itself. For a brief moment, it looked like François Hollande and Angela Merkel would paper over the cracks of the European project. Greece would be given a dignified way out of its nightmare. Remain would scrape home. Hillary Clinton would scrape home.

Now the collapse has happened – and in the worst way imaginable. If you want a vision of the future, don’t just imagine Hard Brexit or Donald Trump in the White House. Consider the fact that on 4 December, Austria is likely to elect Norbert Hofer as its President – a man who has been spotted wearing Nazi symbols and has stated that “Islam has no place in Austria”. Marine le Pen’s victory in the French Presidential election in April is far from assured, but if the French National Front pulls it off there may not be much of an EU for Britain to exit.

This march backwards, into a world of nationalism, nostalgia and authoritarianism, rarely comes to us in the form of uniformed street thugs, or even the newly respectable far right. Its defining feature – the scapegoating of immigrants for falling wages, housing crises and declining public services – is a core rhetorical set piece. This political establishment knows what it is doing: when Theresa May promises to scrap the human rights act, or reintroduce grammar schools, she is not just talking about policy or law, but she is promising to take us back to a time gone by.

The past thirty years have witnessed a dramatic redistribution of wealth from the poor to the rich, alongside a firesale of social housing and the end of decent stable employment for millions. Since 2008, median wages have fallen by another ten percent in real terms. The formulation of these problems as an implicit yearning for the past has an objectively conservative function. It means that social deprivation and disintegration can be woven into a narrative that includes, and therefore blames, immigration, tolerance, and advances in civil rights. And yet even on the left, the main point of reference for a better kind of society is, for many, still the post-war settlement of the Clement Attlee government.

The future cannot be allowed to become a toss-up between a bankrupt neo-liberal elite and a 1950s re-enactment society run by the far right. More and more, it is clear that it will fall to the left to provide the alternative. That alternative is primarily about material things – housing, public investment, higher wages, and a redistribution of the power and wealth of the financial system and the extremely wealthy. It is about the radical democratisation, not just of a broken political system, but of the economy as well.

But just as crucial is a principled defence of the liberal advances of the past few decades. The left owes nothing to the politicians and parties who adopted wholesale the privatising, neo-liberal model of globalisation, and who, at least in the UK, happened to tie themselves to greater civil and individual rights and more open borders in the process. But for those borders to close now, in a blind dash to meet prejudices half way, does not just deprive people of hard-won freedoms – it gives further credence to version of reality proffered by the insurgent nationalist right.

To call this an alliance of the radical left with the liberal centre would be to understate the scale of the realignment that must take place. Just as so many of the radicals of previous decades became centrists, there must now be an entire generation of instinctive cosmopolitan liberals who find a home in a new, inclusive radical left.

For days now, a cry has been reverberating around much of the British left: "If Trump can win, Corbyn can." The comparison is dangerous and the electoral calculation so badly wrong that it can barely be serious, but the deep sentiment it expresses is right – only Corbynism, or a force like it, can beat the new far right. To win, the left cannot rely on some generalised moment of turmoil; it must build an electoral base the likes of which it has never built before, made not by triangulating but by the clarity of its vision and the strength of its ideas and activism. There is a way out of the nightmare of nostalgic nationalism – we do not yet know it to be true, but we have to believe it.