Separation of powers
The separation of powers is the principle that the state's three functions — the legislature (makes law), the executive (implements it) and the judiciary (interprets it) — should be exercised by separate bodies to prevent any dangerous concentration of power.
Last reviewed 14 June 2026
Associated with Montesquieu, it underpins the rule of law through checks and balances. The UK has only a partial separation: the executive is drawn from, and sits within, the legislature.
The Constitutional Reform Act 2005 (creating the UK Supreme Court and reforming the Lord Chancellor's role) strengthened judicial independence and the separation between the judiciary and the political branches.
Key cases
- R (Miller) v The Prime Minister [2019] UKSC 41
- Duport Steels Ltd v Sirs [1980] 1 WLR 142
Frequently asked questions
What are the three branches under the separation of powers?
The legislature (makes law), the executive (carries it out) and the judiciary (interprets and applies it).
Does the UK have a strict separation of powers?
No — it is partial. The executive is drawn from and sits within Parliament, though judicial independence is now strongly protected (Constitutional Reform Act 2005).