Last week’s elections may come to be seen as the moment Britain’s two-party system finally disintegrated. Not because Labour and the Conservatives disappeared overnight, but because the old assumption – that British politics naturally swings between two dominant parties – suddenly looks outdated.

These elections revealed something deeper than a midterm protest vote. Reform UK topped the projected national vote share. The Greens surged into second place in several areas, expanded their councillor base dramatically, and entered the Welsh Senedd for the first time. Meanwhile, Labour and the Conservatives suffered historic setbacks, with Labour’s loss of Wales carrying particular symbolic weight after more than a century of electoral dominance.

The most striking thing about these results is not simply the scale of the disruption, but the shape of it. The emerging political divide is no longer primarily Labour versus Conservative. Increasingly, it is Reform versus Green – two parties offering radically different responses to economic insecurity, immigration, and the mounting pressures of human-caused climate change.

That realignment has been building for years. Britain’s traditional parties have struggled to convince voters they understand either the scale of modern crises or the sacrifices required to address them. Reform and the Greens, by contrast, both present themselves as insurgent movements capable of breaking a stale political consensus. They tend to speak to different constituencies, and offer opposing diagnoses of Britain’s problems, but they draw energy from the same collapse in faith in the political centre.

That’s why these elections are unlikely to prove a temporary aberration. Midterm protest votes usually fade. Structural political realignments do not.

The electoral system has amplified Reform’s rise, turning concentrated support into dramatic council gains. Yet the Greens also have genuine reasons for optimism. Their vote share and representation have increased sharply, and they are now represented across every nation of the UK. At a time when climate politics is often treated as electorally toxic, that matters.

The coming years will now produce two very different experiments in local government.

Reform-controlled councils are likely to become testing grounds for an aggressive anti-net zero agenda, culture war politics, and a broader rejection of environmental regulation. Yet Reform’s position on climate remains less coherent than its rhetoric suggests. The party oscillates between denial, delay, and reluctant acknowledgement – particularly when it comes to climate adaptation. Extreme weather, energy insecurity, food supply disruption and infrastructure resilience all pose problems that cannot simply be dismissed as radical “green ideology”.

That unresolved tension may become one of Reform’s greatest vulnerabilities. A politics built around opposition is easier to sustain before responsibility arrives.

Green-led councils, meanwhile, will attempt to demonstrate that a different political model is possible. Some are likely to become showcases for practical local environmentalism and community resilience. But expectations should remain measured. Councils operate under severe financial constraints, and Green administrations will face intense scrutiny, hostile media coverage, and the inevitable mistakes that come with governing.

The Greens also face a subtler danger. Their recent advances, while substantial, were slightly weaker than many supporters expected only weeks ago. Some voters appear increasingly uncertain about whether the party represents a broad-based environmental movement or a narrower form of TikTok politics. That distinction matters enormously.

If the Greens are perceived primarily as moralistic or polarising, they may struggle to expand beyond their current coalition. If, however, they can root environmental politics in everyday concerns – housing quality, food prices, flood preparedness, transport resilience, energy security – they may yet break through into something much larger.

Climate adaptation could become the central dividing line of the next decade of politics. Britain is entering a period where environmental disruption increasingly intersects with geopolitical instability and fragile supply chains. These pressures will not remain abstract – they will shape household finances, public services, migration, insurance costs, and infrastructure.

The parties that can speak credibly about preparedness and resilience – without tipping into panic (or denial) – are likely to define the next political era.

That’s also why coalition-building will become increasingly important. Multi-party politics changes the logic of elections. The question is no longer simply who wins, but who can govern. Informal pacts, local alliances, and tactical arrangements between anti-Reform parties are now likely to become a permanent feature of British politics.

Some version of a progressive “popular front” may emerge before the next general election, perhaps germinating in fragmented local forms. Whether Labour, the Greens, the Liberal Democrats and others can cooperate effectively remains uncertain. But the pressure to do so will intensify if the Reform threat continues to grow.

This creates a profound strategic dilemma for Labour, which isn’t used to sharing the spotlight. The party may yet recover under a different leader, particularly if it embraces a more ambitious reforming agenda of the kind associated with Andy Burnham, but its years-long dominance of progressive politics appears to be over.

Electoral reform, once treated as a fringe constitutional obsession, increasingly looks like the logical endpoint of Britain’s new political landscape (and is notably part of Burnham’s potential offer). Once proportional representation arrives for Westminster elections – and that prospect now feels more plausible than at any point in modern history – the old duopoly will effectively be over.

The deeper point exposed by these elections is that British politics is no longer organised around loyalty to inherited institutions. Voters are searching for parties that appear willing to confront a period of national instability and decline. Reform and the Greens are currently benefiting because they seem newer, clearer, and less compromised than the exhausted parties that dominated the 20th century.

Whether either movement can sustain that insurgent energy once faced with the realities of power is another question entirely.