Separation of powers
The nutshell
Separation of powers means the work of running a country is split up, so no single group holds all the power. In the UK it is split three ways. Parliament makes the laws, the government runs the country, and the courts decide what the law means.
Every fact on this page comes from Parliament's own guides and non-partisan explainers. Each source tag — like HoC — opens where a fact comes from.
The basics
What separation of powers means
Separation of powers is a simple idea. The work of running a country is split between different groups, so no single group holds all the power. Most democracies split it three ways. One group makes the laws. Another group runs the country day to day. A third group decides what the law means when there is a dispute.
The three parts in the UK
In the UK, Parliament makes the laws. This part is called the legislature. The government — the Prime Minister and ministers — runs the country and is called the executive. The courts and judges are the judiciary, which decides what the law means in a case.CU
Why the UK split is not strict
In some countries the three parts are kept firmly apart. The UK is different. The House of Commons Library points out that the UK has no strict separation, because government ministers are also members of Parliament.HoC So the group that runs the country also sits inside the group that makes the laws.
Keeping the courts separate
The courts are the part kept most separate. The Constitutional Reform Act 2005 made judges free by law to decide cases without pressure from ministers, for the first time in almost 900 years.Jud The same changes moved the UK's top court out of Parliament. A new UK Supreme Court, separate from Parliament, opened in 2009.Parl
- Splitting power three ways is meant to stop any single group from making the laws, running the country and judging cases all at once
- Because the courts are kept separate, judges can rule on whether the government has acted within the law
- The Constitutional Reform Act 2005 made judges free by law to decide cases without pressure from ministers
- The House of Commons Library notes the UK has no strict separation, because government ministers are also members of Parliament
- A government with a majority in the House of Commons can usually get the laws it wants passed through Parliament
- Parliament stays sovereign, so a court can rule on what a law means but cannot overturn an Act of Parliament
The deep end6 min
The three branches
Political theory usually divides the power of a state into three branches. The legislature makes law, the executive carries it out, and the judiciary interprets it. The Constitution Unit at University College London lists the separation of government into executive, legislative and judicial branches among the core principles of the UK constitution, next to the rule of law and the independence of the judiciary.CUThe UK, though, keeps these branches far more tangled than a country such as the United States.
Why the UK has a fusion, not a strict split
The House of Commons Library describes the UK arrangement as one without a strict separation of powers. Government ministers are drawn from Parliament and stay members of it, so the executive sits inside the legislature rather than apart from it.HoC This overlap of the executive and the legislature is what marks the UK out from systems with a firmer divide. Parliament also stays sovereign, so a court can rule on what a law means but cannot overturn an Act of Parliament.
The 2005 reforms and the courts
The clearest move toward separation in the UK has been around the courts. Until 2009 the UK's highest court of appeal was a committee of the House of Lords, part of Parliament itself. The Constitutional Reform Act 2005 created a separate UK Supreme Court, which UK Parliament describes as splitting those who make the law from those who interpret it. The last judgments in the House of Lords were given in July 2009, and the new court opened on 1 October 2009.Parl
The same Act reshaped the role of Lord Chancellor, a post that had once bridged all three branches. According to the Courts and Tribunals Judiciary, judicial independence was enshrined in law for the first time in almost 900 years, and the role of head of the judiciary passed from the Lord Chancellor to the Lord Chief Justice.Jud Ministers now have a legal duty to uphold the independence of the courts and must not seek to sway a particular judicial decision.