Separation of Powers

Defining the theory of the separation of powers


  •      The traditional notion of the separation of powers holds that in order to balance the power in a state and maintain the liberty, the division of powers must be preserved.


The basic idea


  •      Baron de Montesquieu in L’Esprit des Lois stated the following:

 “When the legislative and the executive powers are united in the same person, or in the same body of magistrates, there can be no liberty… Again, there is no liberty if the power of judging is not separated from the legislature and the executive”.



  •      John Locke argued that “there can only be but one Supreme Power, which is the legislative, to which all the rest are and must be subordinate”.


Separation of powers in the UK Constitution


  • The UK is a parliamentary democracy. Therefore, there is an overlap between the executive and legislature in principle.


  • The Constitutional Reform Act 2005 clearly strengthen the judicial power and reduced the executive power.



Constitutional relationships subject to the doctrine


Legislature and Executive


  • Separation of powers is at its weakest in Parliament and government as Parliament provides the personnel for government (fusion of powers).


Henry VII powers


  • The executive can fill in the gaps of statutory schemes. However, there has been an increase in governments using delegated legislation to deal with policy and detail.


  • Henry VII powers allow a minister to make a secondary legislation to amend or repeal Acts of Parliament.


Legislature and judiciary


  • It is a constitutional convention of the highest importance that the legislature and the judicature are separate and independent of one another, subject to some ultimate rights of Parliament over the Judicature. 


Executive and judiciary


  • Both the executive and judiciary can make laws. There is no functional separation of powers. Executive decision making has increased in recent years.


Checks and balances


  • Capstick explains that the legislation in the United Kingdom is not generally subject to external checks by the courts, however, by the representative institutions of liberal democracy.


Relevant Case Law:


R v HM Treasury, Ex parte Smedley (1985) 1 QB 657


Campaign for Nuclear Disarmament (CND) v Prime Minister and others (2002) EWHC 2712


R (on the application of Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5


R (Miller/Cherry) v The Prime Minister [2019] UKSC 41


R v Secretary of State for the Home Department ex parte Fire Brigades Union (1995) 2 AC 513


Entick v Carrington (1765) EWHC KB J98


Burmah Oil v Lord Advocate (1965) AC 75


R (Miller) v Secretary of State for Exiting the European Union (2017) UKSC 5