Jean Monnet, one of the European Union’s 1950s founding fathers, foretold that in a globalised era, size would count. “Our countries have become too small for the world...measured against America and Russia today and China and India tomorrow,” he once said.

Europe’s leaders have since sought to expand the EU in line with this vision. But enlargement, often cited as the club’s most successful policy, has become a political liability. On Thursday, at a summit in Brussels, the EU’s member governments will clash over how much further – and how quickly – the Union can extend to the east.