If you were really concerned about losing national sovereignty, as the UK Leave campaign claims to be, then you would logically need to leave lots of other international organizations, not just the EC. The WTO, Inmarsat, the International Maritime Organization, Interpol, the International Criminal Court, even the International Cricket Conference all impose obligations on their members and compromise their sovereignty.  What would British life be if the country were not in any of these organizations? Let us take just one example – The International Telecommunications Union, and it’s European analogue, ETSI. It it perfectly possible for a country to have its own mobile telephony standards – Japan and the Scandinavian bloc are past examples.  But customer roaming between nations then becomes difficult, and costs of every component part will be higher, due to a loss of scale economies.  Even just operating a common mobile standard but at a different frequencies limits roaming, as anyone alive in the 1990s and traveling between the USA and Europe will recall.