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Principle: Separation of Powers

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  • separation of powers is one of core principles of UK constitution
  • doctrine based on idea that legislative, executive and judicial powers of government should be exercised by separate institutions
  • prevent absolute power being held by any individual or group


  • Montesquieu defined government as three distinct functions: legislative (making of laws), executive (governing according to laws) and judicial (resolving disputes according to law)
  • argued each function should be exercised by independent institutions
  • argued separation of powers enabled liberty
  • .. liberty is a right of doing whatever the laws permit... (Spirit of the Laws (1748))
  • UK context: Parliament (legislative powers), Government (executive function) and independent judiciary

John Locke

  • Locke argued separation of powers needed for effective protection of individual liberties
  • government .. ought to be exercised by established and promulgated laws, that both the people may know their duty, and be safe and secure within the limits of the law, and the rulers, too, kept within their due bounds, and not be tempted by the power they have in their hands to employ it to purposes, and by such measures as they would not have known, and own not willingly... (Two Treatises of Government (1689))
  • particularly concerned there are appropriate checks and balances on the power of the executive to avoid people in power acting in self interest

Critical Analysis

  • tensions within the doctrine and its relationship with core constitutional values
  • highlights distinction between separation and independence
  • functions oneed to be carried out by separate institutions, but all perform a role in creating and upholding law
  • if the laws made by legislature not supported by executive then individuals are unable to rely on the laws and the purpose of the separation is defeated
  • implicit need for coordination between legislative and executive functions
  • if a court was independent to the extent that it did not implement laws made by legislature then there would be no legal certainty and the rule of law would be undermined
  • should be recognised that there is an interrelation between the functions of executive, legislature and judiciary
  • Parliamentary sovereignty allows Parliament to set a framework of law
  • Locke: .. there can be but one supreme power, which is the legislative, to which all the rest are and must be subordinate...
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