Parliamentary sovereignty has several practical consequences in that statues, passed by Parliament may:
- Override constitutional conventions. For example, the Sewel Convention that the UK Parliament will not normally legislate on a matter devolved to the Scottish Parliament can be overridden by statute.[1]
- Amend or abridge aspects of the royal prerogative. For example, the Fixed-Term Parliaments Act 2011 removed the Crown’s prerogative to dissolve Parliament. (And when this Act was repealed by the Dissolution and Calling of Parliament Act 2022, this royal prerogative was revived.)
- Alter the constitution. This right has been long established and can be illustrated with statutes that have changed the constitutional status of Scotland: the Act of Union with Scotland 1707 united England and Scotland under one Parliament and the Scotland Act 1998 established a devolved Scottish parliament.
- Operate retrospectively. There is a presumption that statutes are not intended to have retroactive effect, unless they merely change legal procedure. But with clear words a statute can be drafted so as to operate on matters that predated its enactment. This principle can even apply to criminal law such as with the War Crimes Act 1991, which allowed proceedings for homicide to be brought in Britain against certain persons who had not committed an offence under British law at the time of the alleged offence.[2]
- Override international law. The British constitution adopts a dualist view of international law, which means that each system of law, domestic and international, is treated as a separate legal system. It is for the UK state to determine how, if at all, international laws are applied at the domestic level and there is no impediment on Parliament legislating contrary to international law.[3] Any such legislation would determine a domestic law obligation, although the international obligation (binding on a state) would be unaffected.
For example, in 1951 the UK accepted international obligations that arose under the European Convention on Human Rights. This enabled another signatory state to contend before the European Court on Human Rights (ECtHR) that the UK had breached its international obligations under the Convention.[4] In 1965 individual British citizens were empowered to make such a contention before the ECtHR. It was only with the passing of the Human Rights Act 1998 that (i) the rights established by the Convention became part of domestic law and (ii) accordingly, individuals were empowered to claim in British courts that the Convention had been breached. However, these developments do not undermine the sovereignty of Parliament because Parliament could repeal the Human Rights Act.
[1] This right was recently re-stated by the Supreme Court in Miller No. 1: R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5.
[2] See Retrospective legislation, Research Briefing, House of Commons Library, 2013.
[3] See Principles of international law: a brief guide, Briefing Paper, House of Commons Library, 2020.
[4] The European Convention on Human Rights, article 46(1): The High Contracting Parties undertake to abide by the final judgments of the Court in any case to which they are parties.