We should not forget that besides being an engine for growth, the single market has brought vital political benefits as well. The first is that it has provided a motor for binding political integration among the states of Europe.
As I just described, a single market can only be sustained if there is a common system of laws overseen by a common judiciary – the ECJ. And if there is a judiciary, there must be a legislature to write the law, which in Europe is provided by the EU Council and the European Parliament.