Conventional wisdom says that the political centre is empty. It’s wrong. The liberal centre is held by the traditional third party, which still possesses substantial national infrastructure and resources. The much larger authoritarian centre ground is fiercely contested by the leadership of both major parties, offering competing control narratives in economic and national spheres. What British politics lacks is a Green-Left movement, of the kind that is leading the cosmopolitan backlash to the politics of nationalism and populism.

In Germany, a three-way battle on the left between the hard left, the traditional social democratic party and the Greens has recently seen the latter take the upper hand, aided by its unique ability to take votes from the liberal right. Some commentators see Germany following the path of the Netherlands, where a GroenLinks surge contributed to a fragmented opposition against a single cohesive centre right party. But now some polls even have the German Greens approaching spitting distance of Angela Merkel’s CDU/CSU and staking a plausible claim to major party status.

Their surge comes as much from their overt championing of cosmopolitanism as from their environmentalism. The two go together. The challenges posed by climate change require a fundamental re-evaluation of how we see the boundaries of the nation state. A movement must be built that will fight the case for open borders, one that doesn’t distinguish between the deserving refugee escaping persecution and the underserving “economic migrant” fleeing ecological collapse. It’s a cause that needs a British champion.

So why aren’t the British Greens filling that gap? First Past the Post crushes new parties, but in 2015 extremely dense concentrations of Green support in urban areas put the party in a far better position to make gains than UKIP, who secured almost four times as many votes. But last year’s election has destroyed that; former targets like Bristol West are now some of the safest Labour seats in the country. Statements like this can be hostages to fortune, but the opportunity to make inroads at Westminister seems to have passed for the foreseeable future.

Easily the most successful Green movement within the UK is north of the border; the Scottish Greens outnumber the Liberal Democrats at Holyrood. Their success, however, has been a product of the proportional Additional Member System used for Scottish Parliamentary elections. They have persuaded Labour and SNP voters (particularly the latter group in recent elections; the party has become strongly supportive of independence) to lend their vote on the regional list, but have made no progress in first-past-the-post constituency elections. Indeed, the Greens have been outpolled by UKIP – a peripheral force in Scotland – at the last three Westminster elections.

An ephemeral and patchy record at a local government level across the UK undermines the possibility of growth through Lib-Dem style community-based politics. The European elections that have given the party a steady stream of parliamentarians and funding will come to an end with Brexit. The Greens have never held representation in the Welsh Assembly. The only remaining opportunity for Green success is the London Assembly, overshadowed by the Mayor and soon to be purged of proportionality under the Tory manifesto.

There is no hope of a significant UK-wide Green presence in parliament in the near future. The electoral system has not only played its part in preventing a Green breakthrough but has also deprived the Green party of the chance to cultivate a future generation of leaders beyond Caroline Lucas. Even if first past the post were to be abolished tomorrow, there is no cadre of impressive Green politicians – veterans of devolved parliaments as in Germany or national governance as in New Zealand – to spearhead an overthrow of the status quo.

An effective British Green Left movement will therefore have to work through existing parties, rather than by mounting an external challenge to the party system. While the Conservatives are impenetrable to any lobbying that doesn’t come with a cheque, green influence is already strong in the Liberal Democrats. The two parties have fielded joint slates in London and both have environmental policy as a high priority. It is Labour, however, that offers the largest prize, with open leadership elections for a role conferring leadership of the broad left.

In opposition, Jeremy Corbyn’s environmental aims are laudable. But in power, tensions will inevitably emerge between those goals and Corbyn’s union base in the Labour party, the desire to maintain popularity long enough to remodel the British economy and the need to prove that a nationalised energy industry can deliver savings for consumers. Meanwhile his pursuit of the authoritarian centre ground voter through promises to pour money into police and border security, soft economic nationalism and Euroscepticism, and a cautious approach to welfare could leave him open to a challenge from the left.

Labour’s anti-Corbynites should recognise that so long as the choice facing the party’s members is between him and an unchanged Labour right, he will continue to crush any potential challenge. Green politics could be highly attractive to the Labour party’s disproportionally middle class, urban and environmentally conscious support base. Whether this is first realised by forces internal or external to Labour could prove decisive in the next leadership election.

By winning over the Labour party, an explicitly Green leader might rally the forces of the left and reach across the aisle to right-liberal voters in a way beyond the capacity of the old left or the communitarian Labour right. At the very least a convincing and threatening movement could exert the internal pressure that the defanged anti-Corbynites have been unable to bring to bear. Not all politics everywhere is the same. But it’s hard not to feel that British politics is missing out on the new alternative which many across Europe are starting to embrace.