Sovereignty can be understood as the authority of a state to govern itself, and determine its own laws and policies. In the case of the UK, we also have the idea of parliamentary sovereignty, which holds that Parliament is the highest source of authority to make laws without restriction.
Whilst sovereignty in the first sense may be the starting point for all independent states, sovereignty in the second sense is not. Many states’ parliaments are constrained by requirements of a written constitution, and a constitutional court which can review, and annul laws which conflict with the constitution.
On one level, the UK’s sovereign law-making powers, centred on its Parliament, are challenged by its membership of the European Union, as the UK is constrained in its actions by the agreements it has entered into and laws made under the EU Treaties. At another level, all those constraints are the result of a freely-entered-into decision by Parliament to sign up the EU in the first place.
Almost all countries have international agreements of one kind or another—on trade, human rights or other matters—that constrain governments and/or require changes in domestic law. The World Trade Organisation (WTO), and its agreements, is one such example.
Where the EU differs is that EU law overrides contradicting national law and that disputes about this are ruled upon by a legal authority, the Court of Justice of the European Union, that contains judges from outside the UK. This creates a substantial area of law where Parliament’s power to make unilateral changes is sharply constrained by the overall obligation of EU membership.
Member states can challenge these rulings, but the only way to avoid being directly subject to EU law is to leave the bloc, as the UK plans to do. In other international agreements, disputes are usually resolved by arbitration panels or negotiation between the signatories.View all facts