Statutory instrument
A form of secondary (delegated) legislation made by a minister or government body under powers granted by an Act of Parliament, used to fill in the detail of primary legislation.
Definition
A statutory instrument (SI) is the most common form of delegated (secondary) legislation in England and Wales. Where an Act of Parliament grants a minister or other body the power to make rules, regulations, or orders (an "enabling" or "parent" Act), those rules are made as statutory instruments under the <a href="https://www.legislation.gov.uk/ukpga/1946/36/contents" target="_blank" rel="noopener noreferrer">Statutory Instruments Act 1946</a>. SIs are binding law — breach of an SI can give rise to criminal liability or civil claims just as breach of a statute can. They are published on <a href="https://www.legislation.gov.uk/uksi" target="_blank" rel="noopener noreferrer">legislation.gov.uk</a>. <strong>Parliamentary procedure:</strong> most SIs are subject to either the negative procedure (they become law automatically unless Parliament passes a resolution against them within 40 sitting days) or the affirmative procedure (they must be positively approved by both Houses before taking effect). Some are subject to no procedure at all (made and laid, without a parliamentary vote). <strong>Examples:</strong> the <a href="https://www.legislation.gov.uk/uksi/1998/3132/contents" target="_blank" rel="noopener noreferrer">Civil Procedure Rules 1998</a> (the procedural rules of the civil courts) are made as an SI; the National Minimum Wage (Uprating) Regulations update the minimum wage by SI each year; the Immigration Rules are not technically an SI but operate similarly. SIs can be challenged by judicial review if they are made beyond the powers granted by the parent Act (ultra vires), or if they are incompatible with Convention rights under the Human Rights Act 1998. Courts cannot invalidate an SI on policy grounds — only Parliament can do that.
In practice
When reading a legal citation, "SI 2024/1234" means statutory instrument number 1234 made in 2024. Many of the specific deadlines and requirements you encounter in day-to-day legal matters — court fees, limitation periods for specific claim types, minimum wage rates — are set by SI rather than in the parent Act itself. Always check whether an SI has been updated or replaced when relying on specific figures. The legislation.gov.uk website marks SIs that have been amended. See the <a href="/glossary/statute" class="body-link">statute entry</a> and the <a href="/glossary/judicial-review" class="body-link">judicial review entry</a> for the broader legal hierarchy.