Some people claim that for the UK to join the Single European Currency, the Euro, would involve a loss of sovereignty. Others claim that sovereignty is not lost, just pooled. Some people claim that economic sovereignty is lost but political sovereignty is left intact. Others claim that medium-sized nations like the UK no longer have any economic sovereignty anyway, having lost it to the forces of Globilization and International Capital. There are also those who claim that for the UK sovereignty has already been largely ceded through the Treaties of the European Community.
Matters can appear very complicated.
Many commentators make matters unnecessarily confused by refusing to consider what sovereignty actually is before they start commenting. Instead they will have an idea of what ought to happen and then propose their own definition of sovereignty in their discussions. But really sovereignty is not an elusive or nebulous idea at all. It is in fact quite simple, and the simple concept is sufficient to illuminate the issues. Sovereignty is really a feudal or imperial concept.