There is a real risk that the coming general election could be the United Kingdom’s last – with Boris Johnson remembered only for being its last Conservative prime minister. Johnson’s deal is, we now know, even more fatally flawed than Theresa May’s in vital respects: it threatens to make Ireland a smugglers’ and tax avoiders’ paradise and ushers in a race to the bottom in social and environmental standards. All Labour MPs must vote against it. The deal also threatens to Balkanise Britain. Northern Ireland is, for example, exempted from the evil consequences of a US-UK trade deal – from the entry of chlorinated chicken to the contracting out of NHS services – while Scotland, Wales and England would be bound in.

By the way he has chosen to resolve one source of division, the Northern Ireland border, Johnson appears hellbent on creating another that nationalists are already seeking to exploit. He is jeopardising, perhaps to the point of its destruction, Scotland’s 300-year-old union with England and thus the very existence of the UK.

The extremes now before us – the Johnson deal and an equally hardline 'revoke' – will only exacerbate bitter divisions

So the looming exit is shaping up not as the Dunkirk moment imagined by Brexiteers, with the whole country coming together as one, rolling up its sleeves and glorying in isolation as, united, it faces the foe. Instead it looks like D-day in reverse: a divided, broken-down country retreating from the Europe it once helped to save; and instead of taking control of its future, losing control to the point that it may no longer be able to hold itself together. So when parliament meets on Saturday, the central issue is no longer just what kind of Brexit we have, but what kind of Britain we want to become – and whether there is to be a Britain at all. And the question each party has to ask is: what will it take to heal the wounds of a country now so rent asunder that it qualifies as having many of the features of a failed state?

If the debate on Saturday, and in the coming election campaign, fixates on the two extremes now before us – the Johnson deal and an equally hardline “revoke” – we will only exacerbate our bitter divisions. Just as the Conservatives now discount the views of the 16.1 million who voted remain, so too the Liberal Democrats’ plan to nullify the 2016 referendum without a further peoples’ vote dismisses the concerns of the 17.4 million who voted leave. So it falls to Labour – a remain party that has always acknowledged the real anxieties of leave voters – to set out a path to reunite Britain. The current position of negotiating a better leave package and following it with a second referendum should be updated in the light of Johnson’s existential challenge to the UK. Labour must now propose – and recommend – a renegotiated remain option as well before giving the British people the final say.

There were, of course, many concerns raised in 2016 by Brexit voters: the state of our manufacturing and our industrial towns and a general feeling that our politicians had let us down and lost the plot in the post-imperial era. But the central demands of Brexiteers – directly relevant to our EU membership – were to take back control of our borders and our laws. These demands can now be seen in a new light. In their 2016 negotiations the Conservatives failed – whether out of ignorance, idleness or simply sheer stupidity – to examine in detail the national freedoms already exercised by the Germans, French, Italians and others within EU law. We were, and still are, free to make new choices.

Facebook Twitter Pinterest Labour leader Jeremy Corbyn. Photograph: Sean Gallup/Getty Images

First, it is possible to regain more control of our borders. We could do as Germany does: register migrant workers as they arrive; or, as Belgium does, impose a time limit on any stay without work. In high-unemployment areas, new jobs could first be advertised at local job centres, as in Switzerland. And to stop unfair labour-market competition, whereby the good employer is undercut by the bad, and the bad by the worst, we could end, as France has done since 2016, the practice of “social dumping” and embrace the new German proposal for a European-wide minimum wage. All these objectives are implementable within the general EU principles of freedom of movement alongside enhanced social and environmental rights.

Second, we can ease worries that we have lost control of our laws. We can take more control of our laws in a manner consistent with EU law through domestic legal reform which guarantees the supremacy of the UK constitution. To establish immediate constitutional protections, parliament can issue a “sovereignty declaration” which affirms the UK’s commitment to preserving its constitutional identity in its application of EU law. It could then pass a “sovereignty statute” to guarantee the supremacy of the UK constitution. All this is totally consistent with article 4 (2) of the treaty of Lisbon which requires the EU to respect “national identities”.

Any Johnson Brexit deal sows seeds of future confrontation with the EU | Rafael Behr Read more

So there is a reformed remain offer readily available that I am confident Europe will accept, and which puts not just a botched Brexit – with all its angst, idiocy, and grave economic risks – behind us, but also rejects revoke as a pseudo-solution. Instead we can move ahead confidently, renegotiating – not from weakness, but from strength – a bold new plan to make Europe work for Britain.

For, as this week’s events have demonstrated, it is the ultimate destiny of Britain that will be on the ballot paper when next we vote: whether under a government that looks more and more like the rump of a once national party, we are to be an inward-looking, anti-immigrant, intolerant country, intoxicated by isolation and fragmented by four nationalisms; or whether we are to emerge as a Britain that is outward-looking, tolerant, inclusive and pragmatic, renewing our character as a multinational state, and once again an engaged and visionary leader on the European and the world stage.

• Gordon Brown was UK prime minister from 2007 to 2010