Yet the US, China, Japan and India manage to export successfully to the EU without being part of the Single Market; being inside it is not a straightforward gain. The UK, or any other country that considered leaving the EU, would also have to weigh up what it loses by being a member through having to apply the common external tariff to imports from outside the Union and, most importantly, what it loses from having to apply the rules of the Single Market, and other forms of EU regulation, to those parts of the economy that are not involved in trade with Europe.