Constitutional conventions

Constitutional conventions are the non-legal rules that govern the political behaviour of the principal constitutional actors. They are the rules that determine when the Prime Minister must resign after losing a vote of no confidence; the rule that the sovereign acts on the formal advice of the Prime Minister; the rule that ministers are individually responsible to Parliament for the acts of their departments and collectively responsible for the acts of the Government; the rule (the Salisbury Convention) that the House of Lords does not defeat a Bill implementing a manifesto commitment of the elected Government; the Sewel Convention that Westminster will not normally legislate on devolved matters without the consent of the relevant devolved legislature.

None of these rules is enforceable by a court. None is contained in a single authoritative legal text. Yet they are obeyed nearly all the time, by every actor whose behaviour they regulate, and a serious breach of any of the principal conventions would precipitate a constitutional crisis. The literature on conventions is the literature of the gap between law and practice in a constitution that has no codified text — and on whether that gap is a strength (Bogdanor: flexibility) or a structural defect (Tomkins: opacity).

This week studies the conceptual nature of conventions, the test for identifying them, the leading authorities on their legal status, and the academic debate about codification. The material connects directly to W6 (royal prerogative — exercised on conventional advice), W7 (devolution and Sewel), W11 (constitutional dialogue), and W12 (the constitutional role of the monarch — almost wholly conventional).

The concept of ''convention'' as a distinct constitutional category is the work of A V Dicey. An Introduction to the Study of the Law of the Constitution (1885) drew the modern distinction between ''the law of the constitution'' (rules enforceable in court) and ''the conventions of the constitution'' (''understandings, habits or practices which … regulate the conduct of the … members of the sovereign power''). For Dicey, the two categories were exhaustive and mutually exclusive: a rule was either law or convention, never both, and only law could be enforced.

Dicey''s account was descriptively powerful but conceptually thin. Why are conventions obeyed if they are not law? His answer — that breach of a convention would ultimately bring breach of law in its train, because the political system would respond to constitutional breach by passing legislation against the offender — was unconvincing even to contemporaries. Sir Ivor Jennings, The Law and the Constitution (1933), supplied the more durable account: conventions are obeyed because they are constitutional; they reflect the political principles on which the system runs; their force is the force of constitutional morality, not the threat of legal consequence. Jennings also offered the test for identifying a convention that bears his name and is the modern starting point: (a) is there a precedent of conduct? (b) did the actors believe themselves to be bound by the rule? (c) is there a reason for the rule in the constitutional architecture?

The twentieth-century literature elaborated and refined Jennings. Geoffrey Marshall, Constitutional Conventions (1984), classified conventions by function (rules of formation, rules of operation, rules of dissolution) and pressed the question of how conventions change. Rodney Brazier, Constitutional Practice (3rd edn, 1999), provided the most exhaustive cataloguing. The case-law remained sparse: Madzimbamuto v Lardner-Burke [1969] 1 AC 645 (Privy Council) and AG v Jonathan Cape Ltd [1976] QB 752 (the Crossman Diaries case) were the principal English authorities until the Patriation Reference [1981] 1 SCR 753 in the Supreme Court of Canada became the leading judicial discussion in the Commonwealth. Miller I [2017] UKSC 5 confirmed the Patriation Reference approach in the United Kingdom: the courts will recognise conventions but will not enforce them as legal rules.

Three principles structure modern thinking about conventions.

(1) Conventions are non-legal rules that bind by political (not judicial) sanction. The Privy Council in Madzimbamuto v Lardner-Burke put the orthodox position with characteristic economy: ''it is often said that it would be unconstitutional for the United Kingdom Parliament to do certain things, meaning that the moral, political and other reasons against doing them are so strong that most people would regard it as highly improper if Parliament did these things. But that does not mean that it is beyond the power of Parliament to do such things. If Parliament chose to do any of them the courts could not hold the Act of Parliament invalid'' (per Lord Reid at 723). The architectural point is that the legal validity of an act and its constitutional propriety are different categories.

Five graded practice questions are provided in the Practice Questions panel below — two foundation questions on the Jennings test and the AG v Jonathan Cape principle, two standard questions on Miller I and the codification debate, and one challenge question requiring engagement with Allan and Tomkins.

See the Further Reading panel for the canonical sources from Dicey and Jennings to Marshall, Brazier, the Cabinet Manual, and the recent Miller-era literature.