A no-deal Brexit will cause a disturbing rupture across not just Europe but the west. That’s the stark reality behind Michel Barnier’s slideshow, UK white papers, and the technical article 50 process that encourages us to see it primarily as a bureaucratic and legalistic exercise.

In fact this is a major geopolitical and strategic event. And the prospect of the UK and EU failing to reach agreement on an orderly uncoupling has global implications. So our new foreign secretary, Jeremy Hunt, was right to raise the growing threat of no deal with his German counterpart. The UK and EU have both drawn red lines limiting their negotiating manoeuvres. Each has limited political space for further concessions. The UK took far too long to say clearly what it wanted, and now has probably asked for too much. Time is running out.

The referendum in 2016 settled the question of whether we were leaving or remaining in the EU. The question now is the nature of our exit, and more importantly our future relationship. We tend to fixate on our future economic relations, neglecting the security, defence and home affairs aspects of Brexit. But they are not neatly separable. An acrimonious exit from the EU will have a major economic impact on both sides of the Channel – and it will also damage security and defence cooperation with probably more lasting consequences.

These are not just threats but statements of fact. It is already evident that leaving the EU may lead to a drop-off in operational cooperation on a host of security issues. It’s more than possible to agree to maintain current joint capabilities, but that’s far from inevitable. The current exit deal on offer from Brussels would lead to a significant drop-off on security cooperation, putting lives at risk.

A messy Brexit without any deal would be far worse. It would by definition mean relations had broken down to such an extent that agreement couldn’t be reached even to tie up the terms of our exit, let alone our future. Inevitably, bilateral relations would be soured, leaving Europe damaged.

Some might argue that this is an inherent risk of Brexit, or that it’s the UK’s fault for voting to leave. Perhaps. But the EU isn’t a prison. Under the Lisbon treaty members have a lawful right to choose to leave the EU. Anyway, opposing or regretting Brexit isn’t an answer to the current predicament. Politics and diplomacy are about dealing with the world as it is, not as you want it to be. An accommodation needs to be found.

For understandable reasons EU members have tended so far to trust the European commission to drive the Brexit talks. Their diplomats in London often tell me candidly that their capitals are too distracted to focus on Brexit, and are willing to leave it to Brussels. That needs to change.

A German diplomat agreed that a compromise is needed, but observed that Germany often picked fights on too many fronts

Member states need to give the British decision to leave a little more sober reflection – perhaps when David Cameron came asking for flexibility during his renegotiation it might have been better to give a little more. Now there’s another inflection point where a British prime minister is asking for flexibility.

It’s incumbent on all member states – above all the largest – to focus on Brexit. They need to look beyond the details of customs arrangements and participation in this or that agency, important though they are, to the bigger canvas: the future shape of this continent. And though the UK is but one departing state, it’s Europe’s second biggest economy and its major defence, development and security player. It’s too big to ignore.

Despite the soya bean breakthrough in Washington, President Trump’s trade war with the EU remains a serious threat, and the trans-Atlantic relationship is more strained than at any point since the second world war. Relations with Russia are at their lowest since the cold war, and Turkey is drifting away from the western alliance. Further afield China is slowly shifting its stance and signalling an intention to play a more active global role.

I recently discussed with a senior German source my worry that if Brexit negotiations went wrong, Germany risked a simultaneous “battle” with the US and Russia and a collapse in relations with the UK, at the same time as the EU faced its own internal threats from Poland and Hungary to Italy and the eurozone. And therefore it made sense to find a compromise with Britain based somewhere near the Chequers plan. My friend didn’t disagree, but wrily observed that Germany had often picked fights on too many fronts.

As we leave the EU, the metaphorical width of the Channel is an open question. Berlin, Paris, Rome and the other key capitals should reflect that the UK remains a fundamentally European ally. EU membership was rejected by our political system. But European values aren’t the four freedoms of the single market. They are the respect for the rule of law, liberal democracy, a free press, and powerful institutions – and these run deep through the UK.

There’s still time to agree a fair and sustainable new partnership that works for both sides, and avoids the nightmare of a total collapse in the Brexit process.

• Henry Newman is director of the thinktank Open Europe