Anybody who has worked in Brussels will be familiar with the bicycle theory of European integration. The idea is that unless the EU keeps moving forward, it will fall over and crash.

But the bicycle theory is dangerously out of date. To survive, the EU actually needs to find a brake and a reverse gear. The alternative is a potentially fatal collision between the EU’s institutions and its nations.

The chances of conflict have risen dramatically following a German constitutional court ruling that places Germany in direct confrontation with both the European Central Bank and the European Court of Justice. The German court, based in Karlsruhe, ruled that the ECB’s bond-buying programme — which has helped keep the European single currency afloat — failed a “proportionality test” by not taking into account its broad economic effects. It also stated that the ECJ had been acting beyond its authority, when it declared the ECB’s bond-buying legal.