The law of the United Kingdom is not contained in a single document. It consists of multiple types of legislative instrument, each with a different legal status, a different method of creation, and a different level of Parliamentary scrutiny. Understanding these categories is essential for anyone working with UK legislation, whether as a practitioner, a researcher, or a citizen seeking to understand the law.

Acts of Parliament

An Act of Parliament (also called a statute) is the highest form of domestic law in the United Kingdom. It is a Bill that has been approved by the House of Commons and the House of Lords and has received Royal Assent. Once enacted, an Act can only be repealed or amended by another Act of Parliament (or, in limited circumstances, under the Parliament Acts 1911 and 1949).

Acts are divided into two main categories:

Public Acts

Public general Acts apply to the population at large or to a significant class of persons. They make up the vast majority of legislation and include major reforms such as the Human Rights Act 1998, the Constitutional Reform Act 2005, and the Equality Act 2010. Public Acts are cited by short title and calendar year (for example, "Equality Act 2010") and are assigned a chapter number within the year (for example, "2010 c.15").

Private Acts

Private Acts confer powers or benefits on specific individuals or organisations rather than the public at large. They were historically common for establishing companies, granting land rights, or authorising infrastructure projects (such as railways and canals). Private Bills go through a different Parliamentary procedure, including the opportunity for affected parties to petition against the Bill. While less common today, private Acts continue to be passed, particularly for major infrastructure projects and local authority matters.

A related category is the hybrid Bill, which combines features of public and private Bills. A hybrid Bill affects the public generally but also has a particular effect on specific private interests. The High Speed Rail (West Midlands – Crewe) Act 2021 is a recent example.

Statutory Instruments

Statutory instruments (SIs) are the most common form of secondary legislation. They are made by government ministers under powers delegated to them by an Act of Parliament (the parent or enabling Act). SIs contain the detailed rules that give practical effect to the broad framework established by the parent Act.

The creation, numbering, and publication of statutory instruments is governed by the Statutory Instruments Act 1946. SIs are numbered sequentially within the calendar year (for example, "SI 2014/1" is the first statutory instrument made in 2014).

Parliamentary scrutiny of SIs varies depending on the parent Act:

• Affirmative procedure: the SI must be approved by a vote in both Houses of Parliament before it comes into force (or, in urgent cases, within a specified period after being made). This procedure is reserved for matters of greater significance. The parent Act specifies which procedure applies.
• Negative procedure: the SI is laid before Parliament and will automatically come into force unless either House passes a motion to annul it within a specified period (usually 40 sitting days under s.5 of the Statutory Instruments Act 1946). Most SIs are subject to the negative procedure.

The Joint Committee on Statutory Instruments (JCSI) scrutinises all SIs for technical defects (such as incorrect use of delegated powers, unclear drafting, or failure to comply with laying requirements) but does not consider the policy merits.

Orders in Council

An Order in Council is a type of secondary legislation made by the Privy Council (formally, by "His Majesty in Council"). There are two distinct types:

• Statutory Orders in Council: made under the authority of an Act of Parliament. These function similarly to other statutory instruments and are subject to Parliamentary scrutiny. They are often used for constitutional matters, such as extending legislation to Crown Dependencies or amending the membership of public bodies.
• Prerogative Orders in Council: made under the Royal Prerogative, without statutory authority. They are used for matters such as the governance of certain overseas territories. Because they derive from the prerogative rather than statute, they are not subject to the same Parliamentary scrutiny, though they can be challenged by judicial review.

Devolved Legislation

Since 1998, legislative power over certain matters has been devolved to the Scottish Parliament, Senedd Cymru (the Welsh Parliament), and the Northern Ireland Assembly. Each devolved legislature produces its own primary legislation within the areas of competence defined by the relevant devolution Acts.

Acts of the Scottish Parliament (asp)

The Scotland Act 1998 established the Scottish Parliament and defines its legislative competence. The Scottish Parliament may legislate on all matters that are not reserved to Westminster (Schedule 5 of the Act lists reserved matters, including defence, foreign affairs, and the constitution). Acts of the Scottish Parliament are cited as "asp" (for example, "2020 asp 5").

Acts of Senedd Cymru (asc)

The Government of Wales Act 2006 (as amended by the Wales Act 2017) confers legislative competence on Senedd Cymru. The Senedd may legislate on matters that are not reserved to Westminster (Schedule 7A lists reserved matters). Acts of Senedd Cymru are cited as "asc". Prior to the Wales Act 2017, Welsh primary legislation took the form of Acts of the National Assembly for Wales ("anaw").

Acts of the Northern Ireland Assembly (nia)

The Northern Ireland Act 1998 established the Northern Ireland Assembly and defines its legislative competence. The Assembly may legislate on transferred matters (those not excepted or reserved under Schedules 2 and 3 of the Act). Acts of the Northern Ireland Assembly are cited as "nia" (for example, "2022 nia 3").

Retained EU Law

Following the United Kingdom's withdrawal from the European Union, the European Union (Withdrawal) Act 2018 converted the existing body of EU law into domestic law as "retained EU law" (REUL). This included EU regulations (which had direct effect), EU-derived domestic legislation (SIs made to implement EU directives), and certain directly effective rights under EU treaties.

The Retained EU Law (Revocation and Reform) Act 2023 provided for the revocation of specific pieces of retained EU law and removed the special status of REUL. Under this Act, retained EU law that was not specifically preserved or reformed by the end of 2023 could be revoked by statutory instrument. The Act also abolished the principle of supremacy of retained EU law and removed the requirement for courts to interpret domestic law in accordance with retained EU case law.

Constitutional Statutes

Although the UK does not have a codified constitution, the courts have recognised that certain statutes have a special constitutional status. In Thoburn v Sunderland City Council [2002] EWHC 195 (Admin), Laws LJ identified a category of "constitutional statutes" which cannot be impliedly repealed (that is, they can only be repealed or amended by express words in a subsequent Act, not by mere inconsistency).

Statutes commonly identified as constitutional include:

• Magna Carta 1215 (in so far as it remains in force)
• Bill of Rights 1689
• Act of Union 1707
• Parliament Acts 1911 and 1949
• European Communities Act 1972 (now repealed)
• Human Rights Act 1998
• Scotland Act 1998
• Government of Wales Act 2006
• Constitutional Reform Act 2005
• European Union (Withdrawal) Act 2018

The concept of constitutional statutes does not affect Parliamentary sovereignty: Parliament retains the power to repeal any statute, including a constitutional one. The practical effect is that a constitutional statute will not be treated as impliedly repealed by a later, inconsistent statute. Repeal must be express.

The Interpretation Act 1978

The Interpretation Act 1978 is the statute that provides general rules for the interpretation of all UK legislation. It defines standard terms used across the statute book (for example, "month" means calendar month, "person" includes a body corporate, the masculine includes the feminine and vice versa), establishes rules for commencement and repeal, and sets out how references to other legislation are to be construed.

The 1978 Act is a consolidation of earlier Interpretation Acts dating back to the Interpretation Act 1889. It applies to all Acts of Parliament and (with modifications) to subordinate legislation. Anyone reading UK legislation should be aware of its provisions, as they affect the meaning of every statute on the books.

Further Reading

For a guide to the legislative process, see How Laws Are Made. For an annotated reference list of important statutes, see Key Legislation. For a searchable legislation database, visit Legislation.uk.

The National Archives maintains the official online database of UK legislation, including all Acts, SIs, and devolved legislation.