What is a Statutory Instrument?

There are two types of legislation in the UK, Primary and Delegated.
Primary legislation is in the form of Acts of Parliament. These Acts of Parliament begin as bills debated in the Houses of Parliament, which become law once both houses and the Monarch have approved the bill. When it comes into force, the Act creates a new law or modifies an existing one.
Delegated legislation is generally drafted by the relevant government department in consultation with relevant bodies and parties, and then becomes law on a specified date without being debated in Parliament. Statutory Instruments are the most common form of delegated legislation. Regulations, Orders, Rules and Codes of Practice are also types of delegated legislation.
A Statutory Instrument is a type of delegated legislation that is created by governmental bodies. It has the status of a compulsory law for those individuals or bodies to whom it applies.