In the United Kingdom, an Act of Parliament is the main form of primary legislation.
A draft piece of legislation is called a Bill and needs to be passed by both Houses of Parliament to be given Royal Assent in order to become an Act and part of statute law.
Public General Acts
A Public General Act (PGA) is an act that applies to the whole country (i.e. the UK or at least one of its constituent countries).
For Public General Acts made after 1963, these are cited by the calendar year and a chapter number, written in Arabic numerals (e.g. 2006 c.4).
For Public General Acts prior to 1963, these were cited by regnal year (e.g. 30 & 31 Vic c.27).
Regnal years are calculated from the date of the monarch’s accession to the throne. Each regnal year finishes on the same date the following year. The system carried on in this format until the monarch either died, was deposed, or abdicated the throne.
A quick reference guide to a table of monarchs and their regnal year can be found online.
The Parliament Acts, although rarely used, provide a way of solving disagreement between the Commons and the Lords. Two prominent Parliament Acts established the supremacy of the House of Commons over the House of Lords.
Parliament Act 1911
The Parliament Act 1911  removed from the House of Lords the power to veto a Bill, except one to extend the lifetime of a Parliament. Instead, the Lords could delay a Bill by up to two years. The Act also reduced the maximum lifespan of a Parliament from seven years to five years.
Parliament Act 1949
The Parliament Act 1949  further reduced the Lords' delaying powers to one year.
Private Acts are laws that apply to an individual or individuals (and are known as Personal Acts) or apply to a specific locality or area (and are known as Local Acts).
The online version of The Chronological Table of Local Legislation (or the Chronological Table of Local Acts) lists every local act passed from 1797 to 2008. It was produced by the Law Commission and Scottish Law Commission.
Personal Acts were passed as a means of allowing an individual or individuals to seek compensation from a specific injustice or to obtain a benefit that was, otherwise, not accessible via statute or common law. Despite their historical use, no Personal Acts have been passed since 1987. 
Examples of Personal Acts range from granting of divorces, the naturalisation or granting of citizenship to foreigners to legal name changes. 
Historically, Local Acts were used to frequently approve the construction of railways, canals, and other infrastructure projects. They were also used to create corporations and grant monopolies.
An Act may come into force immediately, on a specific future date, or in stages.
To see when an Act is due to come into force, see the section within the Act headed ‘Commencement’.
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. 
Acts may be amended by subsequent legislation, most commonly by a later Act.
Acts may also be amended by Statutory Instruments.
Scotland, Wales and Northern Ireland all held successful referendums on devolution in the late 1990s. This led to the establishment of separate Parliaments or Assemblies and the democratic election of officials. 
Devolution granted legislative powers from Parliament to devolved institutions: the Scottish Parliament, the National Assembly for Wales, the Northern Ireland Assembly, and the London Assembly as well as their associated executive bodies.
- Justis, “A Royal Anniversary”: An introduction to regnal years
- "Chapter Five: Table of regnal year of English Sovereigns" Sweet & Maxwell's Guide to Law Reports, 4th ed., 1962, pp. 20-33.
- The Parliament Act 1911, legislation.gov.uk < accessed 12 January 2019 >.
- The Parliament Act 1949, legislation.gov.uk < accessed 12 January 2019 >
- The Chronological Table of Local Legislation, legislation.gov.uk < accessed 12 January 2019 >
- 'Private Acts of Parliament used to change a name', Deed Poll Office < accessed 12 January 2019 >
- The Parliament Acts, Parliament UK Website < accessed 12 January 2019 >.
- Devolved Parliaments and Assemblies , Parliament UK Website < accessed 12 January 2019 >.
- Early English Laws - This projects aims to share almost 150 laws made between circa 600AD and the first issue of the Magna Carta in 1215.
- Official Papers UK Blog
- Open Law - The OpenLaw project aims to compile a database of key cases and to make these available freely to all on the BAILII website.
- Parliamentary Archives: Inside the Act Room
- British History Online - a project by the Institute of Historical Research at SOAS documenting printed primary and secondary sources in a digital library.