In the United Kingdom, Statutory Instruments (SIs) are the most common form of secondary or delegated legislation.
Statutory Instruments are governed by the Statutory Instruments Act 1946.  Prior to 1948, local SIs and delegated legislation were known as Statutory Rules and Orders (SR&Os).
SIs are cited with the calendar year and serial number i.e. 1995/246
SIs are often made with authority given by an Act of Parliament, which provides powers to make, confirm, or approve legislation.
SIs come in the form of:
- Commencement Orders, which bring Acts, or particular parts of Acts, into force.
- An Order in Council, which are SIs for when the monarch exercises executive authority in the presence of the country's executive council. Most Orders in Council regard and concern constitutional matters in Commonwealth countries.
These Statutory Rules and Orders (SR&Os) can be found by searching the London Gazette.
These Statutory Rules and Orders (SR&Os) can be found at The British Library. The title of the collection is "Statutory instruments [of a local nature]". These can also be found at the Bodleian Law Library which operates a document delivery service.
Published SIs after 1987 are primarily available on the legislation.gov.uk website or in printed versions.
SIs are known by different terms in devolved governments.
In Northern Ireland, delegated legislation are known as statutory rules, rather than statutory instruments.
Instruments in Scotland made by the Scottish Government are classed separately as Scottish statutory instruments.
Commencement information of the SI is stated on the first page, below the title.
SIs are often effectively almost immediately and usually after they have been numbered, catalogued, and published (in print and online) by Her Majesty's Stationery Office.
Printed copies of a statutory instrument will generally be on sale within a week of the date it is made.
In addition to the main numbering system, there is a subsidiary numbering systems indicating an instrument's position within a particular series of instruments (in the following list n indicates the number):
|Subsidiary numbering system||Note|
|(C n)||Commencement and/or Appointed Day orders which bring into force an Act or part of an Act.|
|(L n)||Legal series: relating to fees or procedures in courts in England and Wales.|
|(S n)||Scottish series: instruments made by the United Kingdom Government which apply to Scotland only (these are different from Scottish statutory instruments made by the Scottish Government under its devolved powers).|
|NI n)||Northern Ireland series: Orders in Council made by the United Kingdom Government under its "direct rule" powers (delegated legislation made by Northern Ireland Departments is made by Statutory Rules).|
|(W n)||National Assembly for Wales series: statutory instruments made by the National Assembly for Wales and applying to Wales only. Welsh language versions are numbered (Cy n).|
Like Acts of Parliament, Statutory Instruments are issued individually and then collected into annual bound sets in numerical, chronological sequence. Prior to 1960, SIs were arranged by subject and were printed annually by Her Majesty's Stationery Office.
- "Statutory Instruments Act 1946" legislation.gov.uk