The European Union and the UK are on a cliff edge. Left to its Brussels-based establishment, the EU continues to turn against most of its people who, as a consequence, turn against Brussels. Meanwhile, facing an immensely damaging Brexit, the people of Britain are becoming despondent. This is the moment for British and continental progressives to forge a close alliance.

Next year’s European parliament elections will not, sadly, be contested in Britain. And they are not capable of toppling the current EU regime, since the European parliament has no such authority. Nevertheless, this vote involving the electorates of 27 member states offers us a splendid opportunity to have the debate that we have been denied so far across Europe.

As with climate change or tax avoidance, solutions cannot emerge either from the British establishment or from Europe’s pseudo-technocracy

Britain’s people – indeed, its MPs – never got a chance to debate the relationship they want the UK to have with the EU post-Brexit. Similarly, the peoples of mainland Europe have never had an opportunity to debate the clear and urgent changes that the EU needs to implement if it is to become a force for good.

We think that we have a duty to spearhead these debates in both Britain and on the continent, using the European parliament elections as our focal point. We also think that this is an opportunity to heal the rift between progressive remainers and leavers in Britain, as well as between continental progressives who have given up on the EU and those who disagree that the EU’s disintegration is the right agenda to take to Europeans.

To this end, we have decided not only to contest European elections in May 2019 on the strength of a single manifesto, mapping out a clear path to a democratic, ecological, egalitarian and ambitious Europe, but also to campaign in Britain. Naturally, we intend to do so in association with our natural allies in the country: Jeremy Corbyn’s Labour party, our colleague Caroline Lucas, leader of the Green party, and other progressives in England, Scotland, Wales and Northern Ireland.

Why campaign in the UK? To what effect? We believe strongly that a common crisis is undermining our societies and our democracies. As with climate change or tax avoidance, solutions cannot emerge either from the British establishment or from Europe’s pseudo-technocracy. “More of this Europe” won’t do the trick, nor will re-nationalisation of policy. What we need, in the UK and in the EU, is a combined municipal, national and pan-European strategy to tackle our common crises: private and public debt; the low levels of investment that contribute to precariousness, unemployment and poverty; environmental protection; solidarity with refugees etc.

As Europeans, British, French, Greeks, Italians, Poles and so on, we need to wrest democratic control over both our national and local governments and, vitally, over the European Union’s institutions. To do so, we need a realistic but radical pan-European plan involving all countries, regardless of whether they are in the European Union, in the eurozone, in the European Economic Area or none of the above.

A month ago, in Naples, we joined forces with political parties from Italy, Poland, Denmark and Portugal to agree to contest the May 2019 European elections on the strength of a single manifesto mapping out a clear path to a democratic, ecological, egalitarian and ambitious Europe. Our programme is founded on two pillars: a pan-European economic policy framework amounting to a green New Deal. And a commitment to launch a grassroots assembly process, from villages to cities and high schools across Europe, culminating in a constitutional assembly which, by 2025, will draft the new foundation texts of a democratic Europe.

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Both these pillars are non-exclusive to the European Union and can, therefore, become part of a progressive agenda for a post-Brexit UK. Would it not be splendid if the people of the UK and of continental Europe demonstrated their contempt for the anti-democratic process conducted in the name of Brexit, by erecting an effective alliance upon these pillars? Would this not be the ideal way to overcome the division between remainers and leavers in the UK, as well as between those of us living in the EU and those outside its formal borders? Is the idea of a constitutional assembly process (which interrogates, in parallel, the UK constitution and our awful EU treaties) not a terribly invigorating prospect?

This is why we plan to include UK cities and towns on our campaign trail leading up to the May 2019 European parliament elections.

• Yanis Varoufakis is an economist and the former finance minister of Greece. Benoît Hamon was the Socialist party candidate in the French presidential elections of 2017

• This article is co-authored with Luigi de Magistris, mayor of Naples (DemA); Rasmus Nordqvist, Danish MP (Alternativet); Rui Tavares, former MEP from Portugal (Livre); and Agnieszka Dziemianowicz-Bąk, leader of the Polish progressive party (Razem)