Brexit is the biggest peacetime crisis we have faced and a no-deal Brexit could provoke a national emergency. The depth and scale of the divisions and the narrowness of the majority in favour of leaving the EU mean that the most sensible step would be to put the issue on hold, complete the negotiations and then hold a referendum. Sadly, that option is not available.

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But it is in the next phase of negotiations that the details of the UK’s future relationship with the EU will be fleshed out. Depending on what happens in those negotiations, either we will see virtually no change to our current status – in which case, what is the point of leaving? Or, as is much more likely, the Brexiteers will demand significant changes to reflect their own views – views that will appal and frighten much of the electorate when they realise the enormity of what is being done. In essence, Brexiteers want to dismantle much of what we regard as the underpinning of civilised life in the modern world.

A referendum now would at least give people the chance to react to the realisation that the easy and facile promises of three years ago have evaporated. £350m a week for the NHS has become a £39bn severance cost to leave the EU, every penny of it to be borrowed by the current political generation, but to be repaid by the young people coming after them.

I am opposed to all the compromises on offer, from Norway plus to common market 2.0 and the so-called Canada-style agreement. In one way or another, they would make us second-class citizens in a second-class country. MPs have rightly rejected the threat of no deal, which removes one disastrous option. All the other options, half-in half-out, satisfy no one. Only another referendum would give us a chance to stay in and pursue the course we have followed with such success over the past 50 years.

Play Video 6:17 'People’s vote' march: up close with anti-Brexit protesters at the 'biggest ever demo' – video

As I told marchers at last Saturday’s demonstration in London, I dismiss with contempt the image of us as an island wrapped in a union jack, glorying in the famous phrase that captured, for so many, Winston Churchill’s spirit of defiance in 1940: “Very well, alone”. I was there. I saw our army evacuated, our cities bombed, our convoys sunk. Churchill did everything in his power to end this isolation. Alone was never Churchill’s hope or wish: it was his fear.

Now, I look back over the years: 70 years of peace in Europe, 50 years of partnership between the UK and the rest of the EU. The fascists have gone from Spain and Portugal, the colonels from Greece. Now we have 28 democracies working together on a basis of shared sovereignty, achieving far in excess of what any one of us could individually. Never forget that it was the memories of Europe’s war that laid the foundations of the European Union today.

Margaret Thatcher would have been appalled to see Britain excluded from the top table. Theresa May dashed across the Channel last week, only to be excluded from a meeting of our former partners, and presented with a take-it-or-leave-it offer. That is what the Brexiteers have done to our country: a national humiliation, made in Britain, made by Brexit.

Britain cannot run from today’s global realities of a shrinking world menaced by terrorism, international tax avoidance, giant corporations, superpowers, mass migration, the rise of the far right, climate change and a host of other threats. Against them, our duty is to build on our achievements in the areas of peace and security that the EU has given us, to maintain our trade access where it matters and to keep our place at the centre of the world stage.

We have a responsibility to hand over and pass on to a younger generation a country richer, more powerful and safer than that which we ourselves inherited. And doing so in partnership with Europe is our destiny, not fleeing to a lonely world and the delusion that Donald Trump offers us an easy way out.

The House of Commons is divided and that reflects what is happening in every village, every town and every city of the UK. But MPs can still do their job and many will do it above party loyalty. They will do what they believe is right.

That is all the more their duty now, because Theresa May is effectively gone. She is a leader in name only because she no longer has any control over events. I am sceptical about changing the singer unless you change the song, and a Tory leadership race would be another massive distraction, but we are where we are.

• Michael Heseltine is a former Conservative deputy prime minister