We face the biggest peacetime decision in a generation – the public must have the final say on Brexit

Without an opportunity for the public to refuse a deal that is not in the country’s interests, Theresa May will undoubtedly wilt against the Brextremists’ blackmail and bully-boy tactics, as we have seen time and again

As summer begins we know we will be returning in the autumn to what will be the greatest peacetime decision our country has faced in any of our lifetimes. The public cannot be excluded from this decision. It is simply too big to ignore or to leave to politicians permanently at odds with one another.

Why is Brexit so important? Because we are not a national economy, self-sufficient or self-reliant, but a European one with major global links – a lot of which are underpinned by trade agreements that the EU itself has negotiated and operates on our behalf. This means that, without an agreement to replace our current EU membership, 60 per cent of our trade would immediately be adversely affected and millions of jobs and livelihoods put at stake.

We can understand it in this way: the EU is not just a huge free trading area – with tariff and non-tariff barriers largely removed to give equal privileges and access to all its members – it is also a giant factory floor. Manufacturing plants in Britain – Airbus, Jaguar Land Rover, Honda, Nissan and Toyota to name just a few – are closely linked to plants in other European countries by means of sophisticated supply chains and seamlessly connected, just-in-time production, with no barriers standing between them.

We cannot afford any disruption. This is why workers across the country are now becoming increasingly worried about what Brexit means for their jobs. If Britain becomes walled off from this single factory floor as a result of Brexit, manufacturing businesses will have no option, over time, but to scale down or shift production to Europe. The impact on the vast number of small and medium sized enterprises supplying them would be devastating.

At long last, Theresa May appears to understand this reality and the need to prioritise market access and continuity of production over parliamentary sovereignty. But even now she cannot quite bring herself to say so and instead of coming straight out and justifying her position, she pretends that there is still no trade-off between these things.

This is because she remains beleaguered in her own party and in parliament. She is opposed by the clean break Brextremists – Jacob Rees-Mogg and his wing of Tory MPs – who ignore geography, refuse to understand how a modern international economy works and imagine that what we lose in Europe we can easily pick up from the likes of India and China. I used to negotiate trade deals: these far away, fast growing countries, which need us less than those close by, are not going to do us favours. The same goes for Trump’s America.

This is why we need parliament to agree a People’s Vote on the Brexit deal: without it we have no way to counter the Brextremists who, if they have their way, will sacrifice trade and jobs in favour of the illusion of independence which will in fact leave us powerless to defend our interests.

Ms May is determined to present the final deal she is negotiating in the autumn, before we are due to leave next March. At this stage – and the timetable can be extended if necessary to allow a proper vote – the public can compare the terms of membership now and the new deal on offer. Without the sanction of a People’s Vote, and the opportunity for the public to refuse a deal that is not in the country’s interests, Ms May will not be empowered to stand up against the Brextremists’ blackmail and their bully-boy tactics, as we have seen time and again.

Of course, the Brextremists will call this undemocratic – that is what they call anything that doesn’t help them get their own way. But the referendum two years ago instructed the government to start a negotiation for EU exit. It didn’t give it the right to make a shambles of the whole process, to be taken hostage by the Brextremists and then dish up a completely unsatisfactory outcome and demand that the country accepts it, whatever the cost.

What is emerging is a million miles away from the complete British sovereignty plus exact same benefits in trade, in both goods and services, that people were promised originally.

Instead, because the Brextremists have tied Ms May’s hands, we are having to pay through the nose for the pursuit of a half in, half out deal, that only partially protects our trade in goods but not services (which account for over 80 per cent of our economy), gives the EU control of the rulebook without Britain having a say and threatens to re-impose a hard border in Ireland with all the implications for future peace. Oh, and continuation of free movement of people in some form, badged under a different name.

The backstop Ms May needs is the certainty of a People’s Vote by which the public can reject a bad outcome if they choose. The alternative is that we charge on, like the Light Brigade, regardless of the facts, regardless of the change in circumstances and regardless of the deal put in front of us.

The only way to give this whole process any sort of democratic legitimacy is to allow the public a Final Say, as The Independent is calling for. Some will argue this is divisive. But what is more divisive than taking us out of the EU on abject terms, destroying the futures of many young people, without the public agreeing, and having to live with the consequences for generations to come?

It’s time for the public to stand up against the Brextremists and demand a People’s Vote.

Lord Mandelson is a former trade and industry secretary and EU trade commissioner