There is a tide in the affairs of men. Throughout his political career Jeremy Corbyn has fought for Labour’s leadership to honour the views of the membership. Some of the most influential of his staff will not be aware of those struggles as they only joined the party in 2016. Long before, Corbyn, together with Tony Benn and John McDonnell, supported the radical demands of the Campaign for Labour Party Democracy. The most contentious of these was that elected MPs must be accountable to the membership.

Corbyn’s strength has always lain in being at one with the membership. He knew he could stand strong in the face of overwhelming rejection by the PLP because the members were with him. This gave him the mandate to draft the 2017 manifesto which offered economic policies that would transform Britain in favour of the many not the few, and added ten points to Labour’s performance as a result.

The membership today is overwhelmingly in favour of referring the government’s Brexit negotiations to the public, so that voters can deliver a verdict on whether Theresa May’s toxic deal will serve the economic interests of the British people. Labour’s leadership team is not honouring that demand in full. Instead Lexiteers with little understanding of the democratic forces that have shaped Labour, recommend political passivity – effectively backing Brexit. By doing so, they risk handing the baton of leadership on the issue of Europe to those MPs most opposed to Corbyn.

If Corbyn breaks decisively from what the membership has overwhelmingly said they want on the single most important economic and political issue of our times – to stay in the European Union – there are no guarantees they will continue to back him. Instead – they may well look for a new leader who embodies the internationalist values they hold dear.

A second risk is that when and if a referendum is called, the same mistake that was made in 2016 will be repeated. Unless the Labour leadership chooses otherwise, the official campaign will be framed and led by those on the right of the political spectrum. If that group – and not say, Laura Parker of Momentum or the groups on the left of Labour who have been campaigning on this issue – is chosen to lead the official campaign to stay in the union, they will benefit from the ability to spend up to £7m. All other campaigns will be less effective as they will be limited to a spend of £800,000. We would lose the opportunity to set out a radical vision of a socialist UK in a socialist Europe, with all the good that could do for the many across the EU.

While it is clear that there are Labour constituencies split on the question of Europe, Labour’s membership is not. Of course there are risks in alienating Labour Leavers. Electorally however the far greater risk to the party would be to alienate Labour’s Remain voters. But this is a perilous time for both Labour’s electoral base and for Britain. Labour members are fully aware of the risks. They recognise that the times require courage and leadership to do the right thing: to acknowledge that membership of the European Union carries costs, but that the costs of Brexit – and especially a chaotic Brexit designed by the Tory Right – to the working people of Britain will be far greater. They understand that the courageous choice is for Labour to commit to stay in the European Union, not for the status quo but to work with social democratic partners across Europe to transform the Union away from the neoliberal economic policies embedded in its Treaties – many of which originated in Britain’s universities, think-tanks and government departments.

A failure of leadership on this issue, will result, we believe, to Labour being punished by the electorate. Every poll over the last year has told the same story – a potential electoral dividend for Labour if we back a second vote and Remain, or a catastrophic loss of support if we allow the Tories to win the Brexit they are so desperate to get over the line. In Scotland, weak leadership over a constitutional issue destroyed Labour as an electoral force in just a matter of years. We cannot afford to let the same happen in the rest of the UK over Brexit.

Millions of Labour’s new voters – overwhelmingly the young – may well switch their support to the Green or Lib Dem parties. A poll of Labour’s 41 most marginal constituencies recently showed us losing 40 of them if we failed to back Remain – the Remain vote splintering to the Greens, Lib Dems and SNP while the Tories held on to their Leave vote. While not dewy-eyed about the EU, these voters are nevertheless clear that Britain will gain more from building alliances with socialists across Europe to tackle global corporations, tax avoidance, crime and the greatest threat to Britain’s security: climate breakdown. They cannot understand why Labour MPs offer tacit support to the far right of the Tory party.

To fail to exercise progressive leadership on this crucial issue is to imperil the Corbyn project. It would take decades before the left could recover from such a defeat.

The Left EU Strategy and Policy Commission, which I chair, urges Jeremy Corbyn to honour the democratic struggles and achievements of Labour’s grassroots members. We call on him to announce immediately that he will respect the overwhelming mandate of Labour’s membership – for the right of the British people to have a final say on their future – to deliver a verdict on the government’s negotiations.

Above all, he must commit the Labour party to both support and lead the national campaign to stay within the EU. And, as the only popular social democratic leader in Europe, commit to work with partners to reform and transform the European Union.

To quote Shakespeare, “On such a full sea are we now afloat”. And on that turbulent political sea Labour must “take the current when it serves, or lose our ventures”. The future is ours to make. But to achieve our goals of cementing the left as the holders of power in the Labour Party, and to gain power in government and influence in Europe we have to choose the path of democracy, and the path of continued EU membership.