Compass warmly congratulates Hannah Spencer and the Greens on their by-election victory in Gorton and Denton last night.

It was spectacular. It was a victory for radical hope and a defeat for Reform. The consequences for progressive politics could be seismic.

It looks as though we are finally witnessing the end of the two-party stranglehold on British politics. This is something Compass has long predicted, welcomed and prepared for. The era of mass, catch-all parties of the left and right could never survive the complexities of a world in which choice, variety and identity have become so pronounced. The future, as we have always said, will need to be negotiated across many parties, not imposed by one. That future is now with us.

A Green vote can no longer be dismissed as a wasted vote, and Labour can no longer continue heading right on the presumption that it faces no serious electoral threat from its left. Indeed, Labour’s long-standing strategy of presenting itself as the only party capable of stopping Reform has been comprehensively undermined in its own heartlands: first in Caerphilly, and now in Gorton and Denton. The politics of fear and lesser-evilism has lost its purchase in a more fragmented landscape with other confident, organised progressives.

But while we celebrate such an important and historic progressive win, we must also confront the challenges it opens up. First, we should recognise that although Reform was defeated last night, they also performed strikingly well.

This seat was more than 400 places down on their target list, and yet they finished a very solid second. The existential threat posed by Reform has not gone away.

Second, the goal is not simply for the Greens to win more seats, welcome though that is, but for progressives together to secure a majority in the next Parliament. The bitter irony is that as the party system fragments, some of its participants can become more tribal. The tricks rolled out in Gorton and Denton, with their share of dodgy bar charts and duplicitous leaflets, are the tip of the tribal iceberg.

The risk of progressive votes splitting and producing unnecessary defeats at the next election is real, especially if the ‘Unite the Right’ strategy succeeds and Reform and the Conservatives come to some form of electoral agreement.

On the progressive side, there are at least three parties in contention in England and four in Scotland and Wales. Tactical voting alone in such a scenario is chaotic. Voters cannot be expected to navigate an increasingly fragmented landscape without clarity or coordination. Under our current electoral system, fragmentation risks distortion, division and wasted votes. If this new multi-party politics is to flourish fairly and effectively, we must change the voting system to one based on proportional representation, so that seats reflect votes and cooperation is rewarded rather than punished.

Moreover, tactical voting does nothing to build power, or negotiate how we build the future we want across many parties and movements, it just imposes a blunt tool at the last minute.

We are entering an era in which collaboration across parties will be essential, not just in terms of shared purpose and policy, but in the practical realities of electoral cooperation. A plural, negotiated politics requires institutions that support it. First Past the Post was built for a two-party age; proportional representation is designed for the diverse, multi-party democracy we are becoming.

We have some time, not masses, before the next election. There is still a fight to change the voting system and to build the foundations of a negotiated plural politics.

That is our fight.

Finally, Labour now faces an existential challenge. Compass has said from the outset that the right-wing hyper-faction would damage the party profoundly. It now appears perilously close to having done so. If Labour is to become part of a new left ecosystem, it must both re-embrace progressive politics and commit fully, for the first time, to genuine pluralism. That must begin internally, through the rejection of hyper-factionalism and of the right-wing groups and individuals who have driven it.

After all, these are the people who backed Mandelson but blocked Burnham. Then, and only then, can Labour fully embrace pluralism externally – not least through the adoption of proportional representation, alongside the necessary political action to implement it. In a fragmented political age, changing the voting system is not a technical adjustment; it is a democratic necessity.

This is a good day. Last night’s result was a welcome and uplifting shot of hope. Progressives can win in seats like Gorton and Denton. Now we must work out how we win together across the whole country – and defeat not just Reform, but the causes of Reform.