The EU is a federation of states (Latin foedus, ‘treaty’, from the same root as fides, ‘trust, good faith’). But for how long can such a federation endure a recalcitrant member? At some stage the crunch will come, as it came for Sparta.

In 338 bc Philip II of Macedon, father of Alexander the Great, completed his conquest of the Greek city-states (poleis) and formed them — for the first time ever — into a political federation.