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François Hollande

For France in the postwar period, the UK has been an indispensable benchmark: the ex-imperial, nuclear twin against which to measure ourselves, and vice versa. Now, Brexit spells potential disaster for France, both as a nation state which, along with Britain, has had justified pretensions to punching above its weight, and as a member state of the EU.

David Cameron had been expected to put the renewal of Britain’s nuclear deterrent before Parliament in the weeks following a Remain vote. This is now unlikely. The so-called Successor programme rests on the assumption that the new nuclear force will continue to be based in Scotland. Rushing a decision through Westminster could send a pro-EU and anti-nuclear Scotland into a headlong rush in a different direction — towards independence. At the very least, sorting out the impact of a vote to Leave in England and Wales on the future of the nuclear base at Faslane and of the nuclear deterrent more generally will cost time and money. France is not enthusiastic about being left exposed as Europe’s sole nuclear power while a politically assertive Russia ramps up its own nuclear capabilities.

At the diplomatic level, the UK will not be a dynamic global player, as most of Whitehall’s energies will be devoted to negotiating with the EU. This will limit France’s ability to put forward diplomatic initiatives which often rely on the ability of our two countries to work together as permanent members of the United Nations Security Council, the pinnacle of diplomatic influence. This inevitable collateral damage could turn into something much worse if the UK fell apart with Scotland seceding and Northern Ireland torn between competing allegiances.

In 1992, after the Soviet Union had collapsed, Russia presented its credentials to the UN as the successor state of the USSR, including its seat at the Security Council. This was strongly supported by the members of the UN in general and the west in particular. Would the world and indeed Russia view with similar enthusiasm the claims of a “rump” UK?

So the French are not only worried. They will most likely provide whatever diplomatic support they can. They will also press for the continued implementation of the Lancaster House defence treaty, which binds the two countries in military terms, notably in the crucial area of nuclear warhead stewardship.

At the EU level things are no better. The forces of sovereigntism in many continental countries will enjoy a boost from Brexit. This is already apparent in the Netherlands, one of the six founding states of the European institutions. It is also true of France, not only in the form of the National Front, but also in parts of the mainstream right. “Frexit” remains unlikely, unless other continental countries start rushing towards the exit: for the French, the European project remains more like a marriage than the cohabitation it always was in the eyes of many in Britain. But Brexit will severely limit the room for manoeuvre in Europe of a largely discredited incumbent president, François Hollande, and government.

Ten months before the next presidential election in France, there will not be enough political leeway for a credible and determined push by France and Germany towards a more integrated Europe. Berlin and Paris will want to be seen as trying, but will hardly expect to succeed. The most likely outcome is an EU that more closely resembles the 19th-century Concert of Nations than Jean Monnet’s dream of a United States of Europe. As a result, France will be increasingly torn between continuing to put all its efforts into maintaining a relationship with Germany, in which it is becoming an evermore junior partner, and playing coalition politics with like-minded states in order to balance German influence and power. Before the UK decided to leave the EU, France’s prioritising of the Berlin-Paris pivot was clear, and justifiable in terms of the national as well as the European interest. It was also comparatively easy to defend in the court of public opinion. This may now change, whoever is the next French president, at the expense of European stability and cohesion.

The writer is special adviser at the Fondation pour la Recherche Stratégique, a Paris-based think-tank