What is an act of Parliament?
An act of Parliament creates a new law or changes an existing law. An act is a bill that has been approved by both the House of Commons and the House of Lords and been given Royal Assent by the monarch.
Acts of Parliament are known as primary legislation, as acts do not owe their authority to any higher form of legislation.
Taken together, acts of Parliament and other forms of legislation make up what is known as statute law in the UK. It is one of the most significant sources of the UK constitution.
Acts often establish the main principles of a new law, while allowing government ministers to set out the finer details in secondary legislation.
More information is given about secondary legislation on our website, and on the government's legislation website at: Understanding Legislation - Legislation.gov.uk
How does an act come into force?
The government is responsible for bringing new laws into force once they have been passed by Parliament.
An act may come into force immediately, on a specific future date, or in stages. You can find out when an act will come into force by looking at the section headed ‘Commencement' in the act itself – this is usually among the very last sections of an act.
Sometimes a specific date is not given, and the timing is left to the discretion of the Secretary of State for the relevant government department.
Although Parliament is not responsible for implementing legislation, its committees can investigate how well an act is being implemented by the government and the effect that the new law is having. This is known as post-legislative scrutiny.
Changes to acts
Future changes to an act can be made by the passing of another act although secondary legislation has been used in some circumstances. An act can also be repealed by a later act so that its provisions no longer apply.
Both parliamentary committees and the Law Commission [external website] examine UK laws and can recommend the removal of out-of-date legislation.
Finding the text of acts
Almost all current acts of Parliament are available to read on the government's legislation website: Legislation.gov.uk (external website)
There you can view the original version of the act, as it was passed by Parliament, and the revised version, which includes any changes made since it was first passed. Texts of most acts of Parliament as originally passed since 1800 are also available on the site.
Original acts of Parliament from 1497 are held in the National Archives. To arrange access to original acts, contact the National Archives (external site)
Structure of an act
The front page of an act has its key identifying information: the short title, its year and its chapter number. Chapter numbers are allocated in sequence during a calendar year, returning to No 1 again at the start of each new year, making it the act’s unique identifier.
The long title of the act, containing its purpose and scope, appears just below, followed by the date on which it received Royal Assent. An example is shown below:
Sentencing Act 2026
2026 CHAPTER 2
An Act to make provision about the sentencing, release and management after sentencing of offenders; to make provision about bail; to make provision about the removal from the United Kingdom of foreign criminals; and for connected purposes.
[22nd January 2026]
The following standard introductory words then appear:
‘Be it enacted by the King’s most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:—'
This is followed by a contents list of the section headings in the act. Most acts are divided up into ‘parts’, each with their own subject heading, so that you can navigate the contents more easily. Very large acts may be divided further, into chapters that each contain several parts. At the end of all the sections, there may be a list of schedules.
The full text of the act then follows, starting at section one. The final sections usually contain general practical provisions that apply to the whole act, including its 'territorial extent' - such as whether the act applies to the whole UK or to just England & Wales, and its ‘commencement provisions’ - when it will come into force.
Commencement provisions may state that sections in the act will come into force on the day of Royal Assent, at a specified point in the future or on a date to be decided by the responsible government minister.
Where additional detail is intended to accompany a particular part of the act, it can be added in a schedule. If schedules have been used, their text appears at the very end of the act.
Since 1999, explanatory notes have been published alongside most acts. These set out the background to the act and what it sets out to achieve. They also explain the text of the act in plain English. You can access explanatory notes on the Legislation.gov.uk (external website).
Find out more about bill and act papers.
Printing of acts
In 1849, Parliament switched from handwriting acts of Parliament to printing them. Since then, the printed acts have been produced on vellum—a durable material made from calfskin—and they continue to be printed on vellum to this day.
Find out more in the Commons Library briefing: Vellum: printing record copies of public acts.
Before the printing of bills began in 1849, acts of Parliament were handwritten. After a bill passed the report stage in one House, it was copied onto parchment. All later amendments—during the third reading and in the second House—were manually added to the same document. Once the bill received Royal Assent, that parchment became the official act. This process was used from 1497 to 1849, so anyone who would like to read bills from this period should consult the final act itself.
Some printed bills from the early 1700s do exist, but they were not produced consistently. Many were printed by private individuals, not Parliament, and often lack details about which stage of the legislative process they represent. As a result, their reliability and usefulness varies.