There is no single law structure of the United Kingdom, rather, it has three distinctly different legal systems, each of which derives from a particular geographical area for a variety of historical reasons: English law (in the joint jurisdiction of England and Wales), Scots law and Northern Ireland law."The UK has three legal systems, operating in England and Wales, Scotland and Northern Ireland"], direct.gov.uk, accessed 12 March 2007 As a result, there is no single unified legal system of the United Kingdom as a result of the continuation of the separate legal systems of England (and Wales), Scotland and Northern Ireland.

In fulfilment of its former EU treaty obligations, European Union directives had been transposed into the UK legal system on an ongoing basis by the UK parliament. Upon Brexit, non-transposed EU law (such as regulations) was transplanted into domestic law as "retained EU law", with an additional period of alignment with EU law during the transition period from 31 January to 31 December 2020. Retained EU law was renamed assimilated Law by the Retained EU Law Revocation and Reform Act 2023.

Since 2007, there have been calls for a fourth type, that of purely Welsh law as a result of Welsh devolution, with further calls for a Welsh justice system.

Legal jurisdictions

There are three distinct legal jurisdictions in the United Kingdom: England and Wales, Northern Ireland and Scotland.  "For the purposes of the English conflict of laws, every country in the world which is not part of England and Wales is a foreign country and its laws foreign. This means that not only totally foreign independent countries such as France or Russia ... are foreign countries but also British Colonies such as the Falkland Islands. Moreover, the other parts of the United Kingdom – Scotland and Northern Ireland – are foreign countries for present purposes, as are the other British Islands, the Isle of Man, Jersey and Guernsey." Conflict of Laws, J. G. Collier, Fellow of Trinity Hall and lecturer in Law, University of Cambridge Each has its own legal system, distinct history and origins, although there is a substantial overlap between these three legal systems and the three legal jurisdictions.

Unlike the other three, Welsh law is not a separate legal system , merely the primary and secondary legislation generated by the Senedd, interpreted in accordance with the doctrines of English law and not impacting upon English common law (except where such Welsh legislation ousts a common law rule by virtue of being a superior form of law).

The UK does not have a single legal system because it was created by the political union of previously independent countries nor has Parliament merged the legal jurisdictions (except for Wales with England). Article 19 of the Treaty of Union, put into effect by the Acts of Union in 1707, created the Kingdom of Great Britain but guaranteed the continued existence of Scotland's and England's separate legal systems. The Acts of Union of 1800, which joined Great Britain and Ireland into the United Kingdom of Great Britain and Ireland, contained no equivalent provisions but preserved the principle of different courts to be held in Ireland, of which the part called Northern Ireland continues to follow as part of the United Kingdom.

Each legal system defaults to its jurisdiction, each of whose courts further that law through jurisprudence. Choice of which jurisdiction's law to use is possible in private law: for example, a company in Edinburgh, Scotland and a company in Belfast, Northern Ireland are free to contract using English law. This is not so in public law (for example, criminal law), where there are set rules of procedure in each jurisdiction.

Structure and history Although Scotland and Northern Ireland form part of the United Kingdom and share Westminster as a primary legislature, they have separate legal systems. (Even though Scotland became part of the UK over 300 years ago, Scots law has remained remarkably distinct from English law). The UK's highest civil appeal court is the Supreme Court of the United Kingdom, whose decisions are binding on all three UK jurisdictions, as in Donoghue v Stevenson, a Scots case that forms the basis of the UK's law of negligence.Donoghue v Stevenson UKHL UKHL

"Great Britain" means England, Wales, Scotland, their adjacent territorial waters and the islands of Orkney and Shetland, the Hebrides and, by virtue of the Island of Rockall Act 1972, Rockall. "United Kingdom" means Great Britain and Northern Ireland and their adjacent territorial waters, but not the Isle of Man, nor the Channel Islands, whose independent status was discussed in Rover International Ltd. v Canon Film Sales Ltd. (1987)(1987) 1 WLR 1597 and Chloride Industrial Batteries Ltd. v F. & W. Freight Ltd. (1989).(1989) 1 WLR 823 "British Islands"but not "British Isles"means the United Kingdom, the Isle of Man and the Channel Islands.

The first schedule of the Interpretation Act 1978, defines the following terms: "British Islands", "England", and "United Kingdom". The use of the term "British Isles" is virtually obsolete in statutes and, when it does appear, it is taken to be synonymous with "British Islands". For interpretation purposes, England includes a number of specified elements: Wales and Berwick Act 1746, section 3 (entire act now repealed) formally incorporated Wales and Berwick-upon-Tweed into England. But section 4 Welsh Language Act 1967 provided that references to England in future acts of Parliament should no longer include Wales (see now Interpretation Act 1978, schedule 3, part 1). But Dicey & Morris say (at p28) "It seems desirable to adhere to Dicey's (the original) definition for reasons of convenience and especially of brevity. It would be cumbersome to have to add "or Wales" after "England" and "or Welsh" after "English" every time those words are used." the "adjacent islands" of the Isle of Wight and Anglesey are a part of England and Wales by custom, while Harman v Bolt (1931)(1931) 47 TLR 219 expressly confirms that Lundy is a part of England. the "adjacent territorial waters" by virtue of the Territorial Waters Jurisdiction Act 1878 and the Continental Shelf Act 1964 as amended by the Oil and Gas (Enterprise) Act 1982.

England and Wales

English and Welsh law (or just English law) refers to the legal system administered by the courts in England and Wales, which rule on both civil and criminal matters. English and Welsh law is based on the principles of common law. English and Welsh law can be described as having its own legal doctrine, distinct from civil law legal systems since 1189.

There has been no major codification of the law, rather the law is developed by judges in court, applying statute, precedent and case-by-case reasoning to give explanatory judgments of the relevant legal principles. These judgments are binding in future similar cases (stare decisis), and for this reason are often reported in law reports.

The courts of England and Wales are headed by the Senior Courts of England and Wales, consisting of the Court of Appeal, the High Court of Justice (for civil cases) and the Crown Court (for criminal cases). The Supreme Court is the highest court in the land for both criminal and civil appeal cases in England and Wales (also in Northern Ireland cases and civil cases in Scots law) and any decision it makes is binding on every other court in the same jurisdiction, and often has persuasive effect in its other jurisdictions.

On appeal, a court may overrule the decisions of its inferior courts, such as county courts (civil) and magistrates' courts (criminal). The High Court may also quash on judicial review both administrative decisions of the Government and delegated legislation. Before the Supreme Court of the United Kingdom was created in October 2009, the highest appellate body was the Appellate Committee of the House of Lords, usually just referred to as "The House of Lords".

After the Acts of Union, in 1707 English law became one of two legal systems in different parts of the same United Kingdom and has been influenced by Scots law, most notably in the development and integration of the law merchant by Lord Mansfield and in time the development of the law of negligence. Scottish influence may have influenced the abolition of the forms of action in the nineteenth century and extensive procedural reforms in the twentieth. Since the accession of the United Kingdom to the European Communities in 1973, English law has also been affected by European law under the Treaty of Rome.

Wales

Welsh law is the primary and secondary legislation generated by the Senedd, using the devolved authority granted in the Government of Wales Act 2006, amended substantially by Wales Act 2014 and Wales Act 2017, and in effect since May 2007. Each piece of Welsh legislation is known as an Act of Senedd Cymru.

As there is no criminal law within contemporary Welsh law, Wales is not generally considered a fourth jurisdiction of the United Kingdom. This is because the judiciary and the courts follow England and Wales law, which is made by the Parliament at Westminster, and is not specific to Wales. Although Welsh law is recognised as separate in operation, this is not sufficient for Wales to constitute a separate legal jurisdiction.

A commission set up in 2017 by the First Minister of Wales known as "The Commission on Justice in Wales" and chaired by Lord Thomas of Cwmgiedd, looked into the operation of justice in the country. Its aim was to further clarify the legal and political identity of Wales within the UK constitution. The commission's report was released in October 2019 and recommended the full devolution of the justice system. This would formalise Wales as the fourth jurisdiction of the UK.

There have been multiple calls from both academics and politicians however for a Wales criminal justice system.

Northern Ireland

The law of Northern Ireland is a common law system. It is administered by the courts of Northern Ireland, with ultimate appeal to the Supreme Court of the United Kingdom in both civil and criminal matters. The law of Northern Ireland is closely similar to English law, the rules of common law having been imported into the Kingdom of Ireland under English rule. However, there are important differences.

The sources of the law of Northern Ireland are Irish common law, and statute law. Of the latter, statutes of the Parliaments of Ireland, of the United Kingdom and of Northern Ireland are in force, and latterly statutes of the devolved Northern Ireland Assembly. The courts of Northern Ireland are headed by the Court of Judicature of Northern Ireland, consisting of the Northern Ireland Court of Appeal, the Northern Ireland High Court of Justice and the Northern Ireland Crown Court.

Below that are county courts and magistrates' courts. The Supreme Court is the highest court in the land for both criminal and civil appeal cases in Northern Ireland and any decision it makes is binding on every other court in the same jurisdiction and often has persuasive effect in its other jurisdictions.

Scotland

Scots law is a unique legal system with an ancient basis in Roman law. Grounded in uncodified civil law dating back to the Corpus Juris Civilis, it also features elements of common law with medieval sources. Thus Scotland has a pluralistic, or 'mixed', legal system, comparable to that of South Africa, and, to a lesser degree, the partly codified pluralistic systems of Louisiana and Quebec.