It should concentrate the minds of everyone in Europe that Britain is to launch its withdrawal from the EU just days after the union’s 27 other members marked the 60th anniversary of its founding. Brexit is just one symptom of the profound troubles that have beset the EU in recent times. Yet for all its shortcomings, the EU has been indispensable to peace and prosperity in Europe. As a benevolent if imperfect experiment in shared sovereignty among nation-states, the EU has no parallel in the world. Britain needs the EU to stay strong after Brexit.

Long before the Brexit referendum, Britain behaved as if it wanted one foot in the EU and one foot out. This ambivalence reflected geography, culture and patterns shaped over centuries. The British nevertheless played a valuable role in promoting the EU’s single market, encouraging the admission of newly democratic countries and lending weight to EU foreign and security policy.

Now, by triggering Article 50 of the EU treaty, Theresa May’s government is embarking on a dangerous voyage. If poorly handled, the withdrawal talks may lead to calamitous consequences, including the break-up of England’s 310-year-old union with Scotland and the collapse of peace and stability in Northern Ireland. The effect on the British economy of a botched negotiation would in all probability be severe. Such outcomes would diminish Britain’s influence and reputation just when the post-1945 liberal international order, of which the UK is a vital part, needs strengthening as never before.