Over the next 48 hours, a battle will take place that will settle the future of the Labour party – and arguably the country. Is Labour to be the party of Europe in uncompromising opposition to the rise of an ugly, hard-right, English nationalism? Or will it continue to temporise over Europe, so enabling the centre of political gravity to shift towards the English nationalist right?

The issue that cannot be fudged is the manifesto on which prospective Labour members of the European parliament will fight the elections on 23 May. As it stands , the draft is unambiguously pro a confirmatory public vote on any Brexit deal, with remain as the other option. That is the position of European MEPs, party members and trade unions as it has gone through the varying consultation processes over the last week.

However, it has yet to be signed off by either the leader or the national executive committee, which meets in a special session on Tuesday afternoon. Jeremy Corbyn himself is torn, recognising that trying to weaken the manifesto to conform with his own anti-EU instincts will imply losing touch with much of his base, so that his position may become untenable. But those in his trusted inner circle and many on the national executive committee elected on a Corbyn ticket think that Labour has to sustain its position of ambiguity.

It’s a familiar story, running like this. The party must “respect” the referendum result partly to protect its “working-class vote” from the incursions of Nigel Farage’s English nationalists but also because the democratic outcome of the referendum demands it. Labour must certainly commit to a better Brexit deal than Mrs May’s, but a commitment to a confirmatory public vote on any deal can only be “on the table”, not a central plank of policy.

It won’t do. The right of British politics is becoming an amalgam of strident English nationalism, nostalgic xenophobia and hyper-Thatcherism hiding behind the language of anti-Europeanism that seeks to legitimise those ugly values. The ageing Tory party, already hostage to thousands of ex-Ukip members who have recently joined it, is being pulled magnetically towards Farage’s Brexit party. Tory councillors and activists around the country say they will vote for it, with its promise of a no-deal hard Brexit and national “independence”, something so valuable, declares Farage, that if it means being poorer and internationally marginalised, so be it. It will allow the greater prize of England becoming the country he wants, home to a virulent capitalism and minimal social safety net; to a spirit of anti-immigration and indifference to inequality.

If the Brexit party tops the European poll, be sure the Tory party will force out May over the summer and an English Eurosceptic nationalist, probably Boris Johnson, will take over, arguing for a no-deal Brexit for what is now the very hard deadline of 31 October. As things stand, the EU will offer no more extensions. Strategically, this new Tory leader’s aim will be to assimilate the Brexit party and its agenda; liberal one-nation conservatism will be torched. Such a leader will split the parliamentary Tory party and in the resulting general election Labour is likely to win. Some Corbynites even think that in strategic terms the more the 23 May manifesto can be fudged, the better. In Leninist terms, it is one step back – a setback in the Euro elections by not fully opposing Farage – for two steps forward, a subsequent Labour general election victory.

Britain is engaged in a civilisational battle of values, recognised by party members if not some in the leadership

It is wrong on so many fronts. First, Britain is now joined in a civilisational battle of ideas and values, recognised by party members and unions, if not some in the leadership. Labour cannot betray its core beliefs – the recognition and celebration of international interdependence in the pursuit of justice, solidarity and fighting climate change; tolerance of the other and joy in diversity; commitment to equality and enfranchising workers – for a moment or in any election. It has to be a remain party because that is what it believes and it must beat the Brexit party into second place because there is no clever-clever one step back to take two steps forward.

If Labour is not explicitly for a confirmatory vote, its support will haemorrhage, now and in the future. Change UK, the Lib Dems and the Greens will benefit, but none has the political infrastructure and depth of political support to top the poll. Labour has a responsibility to its values and to an idea of what Britain should be to win.

Arguments about democracy and the case against English nationalism have to be confronted full on. There is nothing new in insisting that democracies must have the right to change their minds. The Athenian parliamentarian Diodotus argued in 427BC that as facts and arguments develop so democracies must revise their judgments – dismissing the counter-argument that it would cause division.

Equally, Labour’s manifesto must link the case for Europe with a passionate case for reform: the two are indissolubly linked. Its 2017 general election manifesto is the nearest we have to the kind of transformative economic and social programme that will address the just grievances of so much of leave-voting Britain. But it is only fully possible within the EU and its growth-enhancing trade relationships, hence the interdependence of reform with remain.

This is where Labour trumps Change UK, the Lib Dems and the Greens, for all their welcome and convinced commitment to remain. Labour has the opportunity to put together a majority coalition, backed by enlightened business and the progressive middle class, for the policy framework the country needs – staying in the EU, transformative economic and social policies and taking on English rightwing nationalism; and so holding the country together.

The Labour party’s national executive has rarely had a more important decision to take. There are 48 hours to stop Farage and all he stands for. The country, as at other times in our history, needs Labour to do the right thing.

• Will Hutton is an Observer columnist