Unlike the United States, which adopted a single written (codified) constitution in 1787, the UK constitution has never been set down in one place at one time. Instead, it has grown through a sequence of separate documents, each responding to a particular political need or crisis, spread across more than 800 years.
The table below sets out the most significant of these, extending to the most recent example of Parliament reshaping a constitutional arrangement through ordinary statute.
| Year | Event/reform | What it did | Outcome |
| 1215 | Magna Carta | Forced on King John by rebellious barons, it established for the first time that the monarch was not above the law. Clauses 39 and 40 guaranteed that no free man could be imprisoned, dispossessed or ruined except by the lawful judgement of his peers or the law of the land. | Most of its 63 original clauses have since been repealed or superseded, but its principle that government must act within the law became the foundation of the rule of law and influenced later documents including the US Bill of Rights. |
| 1689 | Bill of Rights 1689 | Passed after the Glorious Revolution of 1688, it confirmed that the monarch could not suspend laws, raise taxation or maintain a standing army in peacetime without Parliament’s consent, and guaranteed free elections, frequent parliaments and free speech within Parliament. | Established parliamentary sovereignty as the organising principle of the constitution and ended any realistic prospect of a return to absolute monarchy in England. |
| 1701 | Act of Settlement 1701 | Settled the succession to the throne on the Protestant line through Sophia, Electress of Hanover, and gave judges security of tenure, meaning they served on good behaviour rather than at the monarch’s pleasure. | Guaranteed judicial independence, a core element of the rule of law, by removing the monarch’s power to dismiss judges who ruled against the Crown. |
| 1707 | Acts of Union 1707 | Merged the Parliaments of England and Scotland into a single Parliament of Great Britain, while preserving Scots law, the Court of Session and the Church of Scotland as separate institutions. | Created the unitary state that remains a defining feature of the UK constitution, though one qualified since 1998 by the devolution of power to Scotland, Wales and Northern Ireland. |
| 1911 and 1949 | Parliament Acts 1911 and 1949 | Removed the House of Lords’ power to veto legislation, other than a bill to extend the life of a Parliament, replacing it with a delaying power, initially two years, reduced to one year in 1949. Money bills had to receive royal assent within a month regardless of the Lords’ view. | Confirmed the primacy of the elected House of Commons over the unelected House of Lords, reflecting the steady shift of power towards the more democratic chamber of Parliament. |
| 1972 | European Communities Act 1972 | Took the UK into the European Communities and gave EU law supremacy over conflicting UK statute law, allowing EU law to take direct effect without further legislation. | For almost 50 years, made EU law the highest source of the constitution. Repealed by the European Union (Withdrawal) Act 2018 when the UK left the EU on 31 January 2020, ending that supremacy (see the sources section below). |
| 2026 | House of Lords (Hereditary Peers) Act 2026 | Removed the right of the remaining hereditary peers to sit and vote in the House of Lords, completing a reform begun by the House of Lords Act 1999. | A recent, concrete illustration that the constitution continues to be reshaped by ordinary Acts of Parliament rather than through any single, dramatic rewriting. |
Sources: legislation.gov.uk; UK Parliament; House of Lords Library (see Sources section for full references).
Reading down this table, a clear pattern emerges rather than a single decisive break with the past.
- There was no single dramatic moment of codification: each document addressed a specific crisis of its time, from a rebellion against King John to Brexit, rather than a deliberate attempt to write a complete constitution.
- Power moved gradually away from a central monarchy and towards Parliament, and within Parliament towards the more democratic House of Commons, a trend visible from the Bill of Rights 1689 through to the Parliament Acts 1911 and 1949 and the House of Lords (Hereditary Peers) Act 2026.
- The rights of citizens expanded steadily alongside this shift in power, from the due process protections of Magna Carta, to the parliamentary and electoral freedoms of the Bill of Rights 1689, to the judicial independence guaranteed by the Act of Settlement 1701.
- Statute law has repeatedly been the mechanism of constitutional change, which is itself significant: because ordinary Acts of Parliament can create or dismantle constitutional arrangements, the constitution has remained unentrenched throughout its development.
| Check your understanding 1. Using two examples from the table above, explain how the theme of power transferring from the monarch to Parliament is illustrated by the UK’s constitutional development. Guidance: Pick two documents that show a clear before/after contrast, for example the Bill of Rights 1689 removing the monarch’s power to tax or keep an army without consent, and the Parliament Acts 1911 and 1949 curbing the Lords. For each, state what power moved and to whom. 2. ‘The UK constitution developed through one single, dramatic moment of change.’ Evaluate this claim. Guidance: Treat this as a ‘how far do you agree’ question: briefly explain what the claim implies, then set out at least two pieces of evidence against it spread across different centuries, before reaching a judgement in your final sentence. 3. Why might a historian argue that the Bill of Rights 1689 did more than Magna Carta to establish the modern UK constitution? Guidance: Compare what each document actually changed in practice: note that most of Magna Carta’s clauses have since been repealed, while the Bill of Rights 1689 established parliamentary sovereignty, a principle still operating today. |
next – the nature of the UK Constitution