An Act of Parliament in the United Kingdom is primary legislation passed by the UK Parliament in Westminster, London.[1][2]
An Act of Parliament can be enforced in all four of the UK constituent countries (England, Scotland, Wales and Northern Ireland). As a result of devolution the majority of acts that are passed by Parliament increasingly only apply either to England and Wales only, or England only. Generally acts only relating to constitutional and reserved matters now apply to the whole of the United Kingdom.
A draft piece of legislation is called a bill. When this is passed by Parliament and given royal assent, it becomes an act and part of statute law.