Sovereignty is not a soundbite, it’s a term of art with a specific constitutional and legal meaning. It relates to where ultimate power rests within a state. In the UK it is settled law that Parliament has been sovereign since the seventeenth century and arguably since Magna Carta. There is no encroachment of sovereignty whatsoever involved in the UK abiding by EU law because the reason, and the ONLY reason we do so is because Parliament has approved of the delegation to the EU of some law making functions in particular areas relating to areas where the EU is competent. ( There are in fact a number of other , more minor, instances where we have delegated law making functions to supra national bodies, such as in the case of notifiable diseases where we abide by the rulings of the WHO and sites of international scientific or cultural significance where we abide by the determinations of UNESCO. The proposed WTO terms would, if adopted, involve a similar acceptance into UK law of regulations made by a supranational body, so I find it piss funny personally that some of the people most keen to leave on WTO terms are also those who bemoan our alleged loss of sovereignty.)
Make no mistake about what sovereignty means. Our Parliament has the power to repeal any EU law it chooses, and if it does so that EU law will no longer be in force in the UK. There may be consequences in doing that, of course, because to do so would place us in breach of our treaty obligations. But that is not something that has anything to do with sovereignty, that is to do with political reality. If Parliament says ‘this EU law no longer applies in the UK’ that is the end of the matter, it no longer applies.
The reason people can’t answer the question ‘how have we lost sovereigny’ Is that we haven’t. The loss of sovereignty argument is advanced purely by those who either don’t know what sovereignty actually means, or do know and are dishonest about the alleged loss of sovereignty.