As the Labour party resumes negotiations with what can only be described as Theresa May’s faction of government, Labour members and voters across the country are increasingly concerned as to what any deal might look like – especially as the local election results are used to justify each and every option. But there is something that all of us in the Labour movement need to keep at the forefront of our minds – something substantive we have learned since the Brexit referendum.

While Brexit voters come from all classes and all political stripes and voted Brexit for many different reasons, the people driving Brexit in the Tory party have a very specific economic agenda – one that is now at the heart of these negotiations. Labour is the party of social solidarity and the Tories want Brexit because they want to destroy social solidarity in Britain. To all intents and purposes, they want to eliminate the Labour movement.

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This is why Labour’s negotiations with May are so difficult. You would think that Labour’s Brexit bottom lines would be a welcome gift for May, delivering a Brexit the country could live with. Developed over many months by Keir Starmer and his team, with the express aim of keeping the party and the country together, Labour’s Brexit proposal is the least worst option. It enables the continued integration of supply chains, keeping business in business and invested in Britain, and avoids a hard border on the island of Ireland, without resorting to the Alternative Reality Arrangements Unicorn.

The problem for May is that the Labour proposals also prevent the UK from dismantling the hard-won protections for workers and the environment that we have through our membership of the European Union. It also stops us entering into the kind of trade agreement with the United States that it has with Canada and Mexico – one that destroyed family farming in Mexico, undermining its entire economy – and put downward pressure on wages in all three countries. Opening our markets to American farming methods, as the US ambassador has called for, will destroy the small-scale farmers who give our landscape its beauty and variety.

Facebook Twitter Pinterest Chesil Beach in Portland, Dorset. EU regulations have ensured Britain’s beaches are less polluted Photograph: Stuart Fretwell/Rex Features

Unsurprisingly, the Tories want Labour to accept a set of soft assurances around these issues. Trust us, we would never attack workers rights, the prime minister is saying. Trust us, we would never do a trade deal with the US that destroys British agriculture or dismantles the NHS, she is promising.

But whatever May says or believes, the reality is that her party and her likely successor wants Brexit because they want to use any future parliamentary majority to return us to the past in ways that EU membership does not allow. They want to be free to carry out trade deals that will damage British industry and rural communities.

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So we in the Labour movement have to be tough here. We need assurances around labour rights and environmental protections that will bind the next government. Not vague personal promises from a lame duck prime minister. We must have what we said we must have: a customs union with the EU that allows British industry and British agriculture to continue to participate in European supply chains and have frictionless access to European markets.

Whatever assurances May can offer, they will not stop the hard-right Tory Brexiteers in their quest to eradicate solidarity from the UK economy. If we are to avoid the fate of Ramsay Macdonald, then any deal must be put to a vote of the people. To do otherwise would be to play either the knave or the fool – and gives Theresa May’s successor the right to decide which we have been.

• Chi Onwurah is the Labour MP for Newcastle upon Tyne Central