After the double shock produced by Brexit and the Chilcot report, we are faced with the wider question of how Britain will redefine its role in the world – and how that role may still depend on the cooperation it can maintain with its European neighbours.

Will Nato’s warmer words prevent a new cold war? | Mary Dejevsky Read more

Last week Nato held a summit in Warsaw, cast as a welcome show of western solidarity at a time when Brexit has placed a huge question mark over transatlantic relations. Nato will remain a pillar of European security, but as Britain starts pulling out of the EU there will be consequences. Historically, Britain has been pivotal to the transatlantic link. Now pressure is mounting for the EU to take more responsibility for its own security, to prevent chaos spilling into its territory from the east and south.

Britain will be faced with stark choices. Cut off from the EU but still inside Nato, it risks becoming an ever more junior partner to the United States. That is a gamble given the current mood of US isolationism, and the possibility of Donald Trump being elected president. Yet engaging with the EU from outside on foreign policy and security issues will require a considerable amount of goodwill on both sides – and there is little on display right now.

Asked how a European framework might have saved Britain from its Iraqi adventure, Robert Cooper, an experienced British diplomat who in 2003 worked with the EU, says: “It’s very healthy for any government to hear different views, and in terms of getting a challenge to your policy, the EU is not a bad place to be.”

Government is essentially introspective. And civil servants aren’t particularly good at telling the truth to their political bosses. As excerpts from the Chilcot report show, Tony Blair was locked in a highly personal relationship with George W Bush (illustrated by the “I will be with you, whatever” note). In 2002-03 Blair never found himself in a room with a group of EU leaders – who would have thoroughly challenged him about how, and why, he planned to resolve the Saddam Hussein problem.

Europe was of course deeply divided over Iraq. The two largest continental powers, France and Germany, were staunchly opposed to the war. Jacques Chirac, then French president, threatened to veto any UN resolution that might authorise an intervention. Gerhard Schröder, the German chancellor, made opposition to the war a key theme of his re-election campaign in autumn 2002.

When the EU forges a common position on a tricky foreign policy issue, it can fine-tune its choices and get things right

This reinforces Cooper’s point. When the EU does try to forge a common position on a tricky foreign policy issue, it can fine-tune its choices and get things right. Take the case of Myanmar: years ago a balance was struck among EU states between tough, US-backed sanctions (which the UK also supported), and the views of those countries, such as Italy, that didn’t want any sanctions at all. In the end, Europe exerted pressure by discouraging investments in Myanmar, but without closing the door to dialogue.

One thing Britain will lose once it is out of the EU is the sustained interaction that comes from taking part in a constant stream of EU meetings: the often tiresome but indispensable routine of trying to find common solutions to common problems. That common diplomatic culture existed for 40 years – with ups and downs – but is about to be dismantled entirely.

Of course, working out a European policy on Myanmar is not the same thing as finding a compromise between war or no war in the Middle East. Iraq set in motion a much deeper clash of interests among Europeans: Britain’s “special relationship” with the US was a key item in that diplomatic battle.

The Iran agreement is a disaster for Isis | Federica Mogherini Read more

But now, with global US power having become more relative, post-Brexit Britain will have to think hard about what it may still want to do with European partners on foreign and security policy – if anything at all. There is talk of strengthening EU-Nato cooperation. Nathalie Tocci, an adviser to Federica Mogherini, the EU high representative for foreign affairs and security policy, believes Brexit will ultimately encourage such a rapprochement – and that would arguably be the only positive outcome of the referendum. Others such as George Robertson, a former Nato secretary-general, are less certain, because the UK’s EU membership has been so central to links between the two organisations.

The EU may not be seen as a heavyweight in foreign policy, but it played an important role in the Iran nuclear deal, and in pressuring Russia with sanctions. The US has repeatedly indicated it wants Europeans to shoulder more of a security role, and not just through Nato. Britain will be out of the EU club but, from terrorism to climate change and migration, none of the international challenges it faces are in any way different from those of its continental neighbours.

The danger is that Britain will now find itself so embroiled in the complexities of its divorce from the EU that it will end up in a hazardous position on the international stage: delusional about its influence on the US, and cut off from the wider European discussions.