|Constitution||Uncodified and unwritten|
|Legal system||Common law: England and Wales; Ireland |
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK), consists of four constituent countries: England, Scotland, Wales, and Northern Ireland.
There are four countries which make up three legal jurisdictions in the UK, with each having its own court system and legal profession. England and Wales have a combined legal system, while Scotland and Northern Ireland have independent legal systems.
The Channel Islands  and the Isle of Man, although part of the British Isles, are not part of the UK, and have their own legal systems.
The United Kingdom is a unified state with a parliamentary government under a constitutional monarchy,  in which the monarch is the head of state of the UK. The parliament of the UK, as the legislative branch, is formed of two houses: an elected House of Commons and an appointed House of Lords.
The position of Prime Minister belongs to the individual most likely to command the confidence of the House of Commons, typically the leader of the political party (or coalition of parties) that holds the largest number of seats. Along with the cabinet, the Prime Minster exercises executive power as part of the formal appointment by the monarch as Her Majesty's Government.
Across the UK, there are four different legislatures and executives, each with a different range of powers.
These devolved powers were granted by the UK Parliament, based in Westminster, to these devolved bodies:
(1) the Scottish Parliament
(2) the Senedd Cymru (Welsh Parliament) 
(3) the Northern Ireland Assembly
These three legislatures, each with their own government, can only pass primary and secondary laws within their devolved areas (or "transferred" in the case of Northern Ireland), with "reserved" matters remaining the responsibility of Westminster. Although, the UK Parliament can still legislate in devolved areas, but, under the Sewel Convention, does “not normally” do so without the explicit consent of the relevant devolved body. 
However, these devolved powers ultimately, and centrally, reside with the UK Parliament and means the legislation which created these devolved administrations can be amended or repealed in the same way as any statute.
The official legislation website, legislation.gov.uk, provides a full text of all public general Acts of Parliament since 1988, and Local Acts since 1991, as well as selected content from 1801 onwards. However, both LexisLibrary and Westlaw are also excellent sources for up-to-date UK legislation (with any amendments incorporated within 48 hours). Westlaw also contains historic versions of legislation dating back to 1991, and LexisLibrary from 1998.
Acts of Parliament are published individually soon after they have received the Royal Assent. At the end of the calendar year, they are reissued in bound volumes as Public General Acts & Measures.
Similarly, Statutory Instruments (SIs) are issued individually and then collected into annual bound sets in numerical, chronological sequence. Prior to 1960, these were arranged by subject. UK statutory instruments are available chronologically on the legislation.gov.uk website from 1987 onwards, with selected coverage from 1947.
There are three distinct systems of law within the UK: English law, which applies in England and Wales, Northern Ireland law, and Scots law.
Both English law and Northern Ireland law are based on common-law principles. However, Scots law is a hybrid system based on both common-law and civil-law principles.
England and Wales
Main Article: Courts of England and Wales
The highest court in England and Wales for both criminal and civil cases is the UK Supreme Court, which replaced the Appellate Committee of the House of Lords in October 2009. Decisions made by the Supreme Court are binding on lower courts, including those in the same jurisdiction. These decisions often have a persuasive effect in other international jurisdictions.
The Judicial Committee of the Privy Council (JCPC), includes the same members as the Supreme Court, and is the highest court of appeal for several independent Commonwealth countries.
Below the UK Supreme Court, the hierarchy of courts in England and Wales are headed by the Senior Courts, which consist of the Court of Appeal, the High Court of Justice (for civil cases) and the Crown Court (for criminal cases). Each of these courts have their own system of lower courts.
Main Article: Courts of Scotland
The highest courts in Scotland are the Court of Session, for civil cases, and the High Court of Justiciary, for criminal cases. However, the UK Supreme Court serves as the highest court of appeal for civil cases under Scots law.
Scots law is also unique in that is has three possible verdicts for a criminal trial: guilty, not guilty, and not proven, in which verdicts of not guilty and not proven result in an acquittal. However, there have been recent calls to reform and abolish the not proven verdict. 
Within the Scottish system, Sheriff courts deal with most civil and criminal cases. Criminal trials conducted with a jury are known as a sheriff solemn court, and criminal trials with a sheriff but no jury are known as sheriff summary court.
Main Article: Courts of Northern Ireland
The Court of Judicature of Northern Ireland is the main body of superior courts in Northern Ireland. It consists of the following courts:
- The Court of Appeal in Northern Ireland (Court of Appeal)
- The High Court of Justice in Northern Ireland (High Court)
- The Crown Court
The title of the courts were changed on 1 October 2009 following the creation of the UK Supreme Court, in which it was previously known as the Supreme Court of Judicature.
The UK Supreme Court is the highest court in Northern Ireland for both criminal and civil appeal cases.
As much of the UK follows a common law system, where much of the case law is developed by judges in courts, who apply statutes, precedent, and common sense to the facts of a case prior to issuing a explanatory judgment of the relevant legal principles, which are then reported. Due to the hierarchy of the court system in the UK, the decisions of higher courts are binding on lower courts and on any future similar cases.
However, the sheer number of cases being heard across the UK, many of the cases which are featured in law reports are usually those of legal importance.
Most cases or judgments are usually available on the major databases. Similarly, coverage of various law reports across these databases varies due to publishing exclusivity.
Unreported cases may exist in transcript form (or requests may be made to transcribe proceedings for a nominal fee). Some cases, however, are uploaded by BAILII (British & Irish Legal Information Institute) due to a direct channel from the courts.
Many cases from 2001 in the UK now also have a neutral citation. These are to identify judgments independently of any series of reports, and cite only the parties, year of judgment, court, and case number.
- The UK is one of two countries in the modern world where there is a constitutional monarchy where the constitution remains 'unwritten' and uncodified - the other is New Zealand.
- The Channel Islands is a geographical, not political, term to describe the Bailiwick of Jersey and Bailiwick of Guernsey, which are Crown dependencies. Guernsey is further divided into sub-jurisdictions: Guernsey, Alderney, and Sark.
- In paraphrasing Thomas Macaulay, political scientist Vernon Bogdanor, in a journal article, has defined a constitutional monarchy as "a sovereign who reigns but does not rule". See The Monarchy and the Constitution, Parliamentary Affairs, (1996) 49 (3), pp. 407 - 422.
- On 6 May 2020, the National Assembly for Wales officially became Senedd Cymru and Welsh Parliament, as per Senedd and Elections (Wales) Act 2020.
- Official announcement - Senedd Cymru and Welsh Parliament names become law, Senedd Cymru website < accessed 8 May 2020 >
- Introduction to devolution in the UK, House of Commons Library < accessed 23 January 2020 >
- The structure of the courts, judiciary.uk < accessed 23 January 2020 >
- Compared to the Italian system for criminal procedure, there are five verdicts, two of which correspond to the Scottish equivalent.