6. Constitutional conventions

Some aspects of the constitution are not derived from legal sources.  For example, there is no statute or common law that says there must be a Prime Minister and Cabinet.  These posts are a constitutional requirement, by convention, rather than law.  In other words they have their source in wisdom and history rather than strict law.


Constitutional conventions have three distinguishing features. They are:

  • rules of constitutional behaviour, which cover things such as who does what and how,
  • considered to be binding on those with constitutional functions, and
  • are not enforced by the courts.


The Monarch:

  • plays no active role in matters of government,
  • has legal powers which are exercised on behalf of the government, often on the advice of government ministers,
  • will not refuse Royal Assent to a bill duly passed by Parliament, and
  • will appoint as Prime Minister the person who is best able to command the confidence of the House of Commons.

Government ministers:[1]

  • will be members of either the Commons or Lords,
  • will take ministerial responsibility for their respective departments in the sense that they must ‘carry the can’ for what their department does (the Carltona principle),
  • are bound by collective cabinet responsibility in that:
    • they must not disagree publicly with government decisions and hence if they wish to do so then they must first resign, and
    • cabinet discussions are confidential.


  • The UK Parliament will not normally legislate on a matter that has been devolved to the Scottish Parliament unless the Scottish Parliament gives its consent (the Sewel Convention).
  • The House of Lords will not oppose the second or third reading of any government legislation that have been promised in its election manifesto (the Salisbury Convention).


  • members of the judiciary must refrain from politically partisan activities, and
  • members of the Executive should respect judicial independence by being restrained when commentating on the words or deeds of judges, though if criticised by a judge they are not obliged to remain mute, and if a judge makes politically controversial remarks a robust answer can be offered.[2]

[1] Ministers are affected not just by constitutional conventions.  Since the Second World War the main laws, rules and conventions affecting their conduct has been set out in a Ministerial Code, which is not intended to have any legal effect.  It is explained by the Institute of Government here.  The Code has been published since 1992 and the current version can be accessed here.

[2] Constitutional and Administrative Law, Stanley Smith and Rodney Brazier, 1989, p375.