Well I am not a leaver but I would see it like this. Sovereignty was the supreme power attributed, in our case, to the Sovereign. Following the Bloodless (it wasn't of course) Revolution and a few other bits of our history we agreed to stop chopping off Monarchs (Sovereigns) heads if they passed sovereignty to Parliament. Not to the government - to Parliament. Parliamentary sovereignty is a principle of the UK constitution and this include the Lords and Commons, the Government and the Opposition.
All bodies who have sovereignty (and any self-governing state does) can trade little bits of it for other things like being in a trading body with other countries or an alliance to be there in time of war. Our Parliament has passed laws to limit their own sovereignty when they devolved power to the Scottish Parliament and Welsh Assembly, enacted the Human Rights Act, joined the European Union in 1973, and established the UK Supreme Court in 2009. All of these decisions took power from Parliament and passed it elsewhere by the agreement of Parliament.
Mrs May has attacked sovereignty on at least three occasions and I have to wonder if she actually understands it. Firstly, she attacked the judiciary because they would not let her have her own way when she was acting illegally and against the sovereignty of Parliament. Secondly by trying nefariously to give Parliaments powers over to the government and thirdly by not informing Parliament as she should.