Conventions are a non legal source of the UK constitution. Conventions tend to govern the relationships between the branches of State – executive (both Crown and Government), legislature and judiciary. They can be seen to extend principles in the Bill of Rights 1689, especially in regard to the relationship between Crown and Parliament. Conventions can be seen as regulating the processes and mechanics of Government in a way that is consistent with the concept of democratic legitimacy. Guidance on the office of Prime Minister and role of the Cabinet are almost entirely found in convention.
Constitutional conventions are not rigid and therefore difficult to define.
Dicey described conventions as
.. The other set of rules consist of conventions, understandings, habits or practices which, though they may regulate the conduct of several members of the sovereign power, of the Ministers, or of other officials, are not in reality laws at all since they are not enforced by the courts. This portion of constitutional law may, for the sake of distinction, be termed 'the conventions of the constitution', or constitutional morality...(Introduction to the Study of the Law of the Constitution (1885)).
Wheare stated that a convention is
.. a binding rule, a rule of behaviour accepted as obligatory by those concerned in the working of the constitution... (Modern Constitutions (1951)).
Sir Ivor Jennings
Jennings argued that
.. the short explanation of the constitutional conventions is that they provide the flesh that clothes the dry bones of the law; they make the legal constitution work; they keep it in touch with the growth of ideas...(The Law and the Constitution (1959)).
Geoffrey Marshall and Grahame Moodie
Marshall and Moodie suggested that conventions are
.. rules of constitutional behaviour which are considered to be binding by and upon those who operate the Constitution but which are not enforced by the law courts... nor by the presiding officers in the Houses of Parliament...(Some Problems of the Constitution (1971)).
There tends be broad recognition of the content of some conventions. These include the conventions that the monarch appoints the leader of the majority party of the House of Commons as Prime Minister, the rules that ministers are individually and collectively responsible to Parliament and that judges will remain politically impartial.
Conventions are usually seen as supplementary to laws but sometimes seem to override legal rules. For example by law the monarch must approve Bills before they become an Act of Parliament however, in practice there is a convention that the monarch will not refuse Royal Assent to Bills passed in both Houses of Parliament. The last time a monarch refused was when Queen Anne declined to give assent to the Scottish Militia Bill 1707. This has led to the suggestion that conventions should be viewed as .
.non legal rules regulating the way legal rules shall be applied... (Marshall and Moodie).
The nature of conventions means that it is difficult to determine when they came into existence or a precise process of creation. Conventions are usually unwritten and therefore it is often necessary to try to identify when they have been generally observed in order to say when have become operational.
Colin Munro puts forward that conventions
.. do not come from a 'certain' number of sources: their origins are amorphous... Nobody has the function of deciding whether conventions exist. There is no formal sign of their entitlement to be so regarded, as there are no agreed rules for deciding.. (Studies in Constitutional Law (1999)).
Most conventions seem to evolve as political procedures before they become recognised a constitutional convention. Therefore most conventions are created organically over time, especially those relating the role of the Crown. However, some can be seen as a result of a specific events, for example, conventions that establish a framework for relations between the UK and Commonwealth countries were set out in Preamble to the Statute of Westminster 1931, after being agreed at a conference.
Jennings proposed a threefold test for the identification of conventions. For a convention to be established the following three elements must be established:
1 What are the precedents?
2 Did the actors in the precedents believe that they were bound by a rule?
3 Is there a constitutional reason for the rule?
This test can be used to decide whether a convention has come into existence, and also whether it has ceased to operate. All three elements must be present if the convention is to be fully established.
Re Amendment of the Constitution of Canada 
A case regarding the Government's proposed constitutional changes. The written Canadian constitution did not require consent of the provinces. However, it was convention that the provinces agreement should be obtained prior before changes were made to the constitution.
The Supreme Court of Canada approved the Jennings Test.
The Court found that
.. the main purpose of constitutional conventions is to ensure that the legal framework of the constitution will be operated in accordance with the prevailing constitutional values and principles of the period... Perhaps the main reason why conventions cannot be enforced by courts is that they are generally in conflict with the legal rules which they postulate and the courts are bound to enforce legal rules... .
As a result of the decision, the Government submitted alternative proposals which were approved by the majority of provinces.
The decision is persuasive in the UK.
Munro has argued the Jennings Test is inadequate, because of lack of clarity over who decides what is a sufficient constitutional reason and it emphasises precedents not recognising some conventions are based on agreements.
Rules are not enforceable by the courts but seem to be largely obeyed. For individual office holders the reasons to obey conventions may include wishing to maintain legitimacy and an acceptance that by taking office there is implied agreement to follow conventions.
Dicey argued that ultimately a breach of convention would lead to a breach of law. He illustrated his point by referring to the convention that Parliament must meet each year and if it failed to do so the authority for the maintenance of the army would lapse (under Article 6 of the Bill of Rights 1689).
.. the breach of a convention carries with it a destructive effect, which is absent with laws.... A convention that is not adhered to does not necessarily cease to exist but may require future affirmation.
Distinction from Laws
Laws and constitutional conventions are interlinked but distinct.
A law be found in an Act of Parliament or in a judicial decision. A convention is a practice that is observed from an undefined point.
A law is written in legislation or a judgment and therefore there is a level of certainty. Most conventions are not written and therefore less easy to determine. For example the convention on Ministerial Responsibility is vague but in comparison the rules of Royal Assent are more established.
A statute must be revised or a judicial decision overturned in order for a change in law to take place. A convention can evolve without any formal process.
Laws are enforceable by the courts. Conventions lack formal enforceability. Dicey states that constitutional convention are
.. not in reality laws at all since they are not enforced by the courts.... Similarly Marshall argues that conventions
.. are unlike legal rules because they are not the product of a legislative or a judicial process.....
A breach of a law has a defined legal sanction but a breach in itself does not affect the validity of the law. A breach of a convention has no legal repercussion but may have a political impact. Munro argues a serious breach of a convention may challenge its effectiveness and even result in the overturning of the convention.
Appointment of the Prime Minister
One of the key constitutional conventions relates to the appointment of the Prime Minister. It is the role of the Monarch to appoint a Prime Minister. Legally, this can be whoever they choose. However, by convention it must be someone who commands the confidence of a majority in the House of Commons. Precedent suggests that the Prime Minister must be either a member of a House of Parliament.
Since 1963 it has become a recognised convention that a Prime Minister should come from the House of Commons, in order to be accountable to the House. There is an exception that a Prime Minister can hold office temporarily whilst not a MP during a General Election.
Conventions and the Courts
Constitutional conventions may not be strictly enforceable in the courts, however, they may still require consideration in cases.
R v Secretary of State for Home Affairs, ex p Hosenball 
Court of Appeal declined to review the Home Secretary's decision to deport a journalist in the interest of national security.
.. he is answerable to Parliament as to the way in which he did it and not to the courts here....
R v Secretary of State for the Home Department, ex parte Cheblak 
Claimant sought judicial review of the Home Secretary's decision to deport him on the grounds of national security.
Again the court recognised the existence of the convention of Ministerial Responsibility, that a Minister is accountable to Parliament for their decisions.
Carltona v Commissioners of Works 
Claimant argued requisition of their factory was invalid. The order requisitioning the factory was made under wartime regulations and had been signed by a civil servant on behalf of a Minister. Signing such an order was a statutory power given to the Minister.
.. Constitutionally, the decision of such an official is, of course, the decision of the minister. The minister is responsible. It is he who must answer before Parliament for anything that his officials have done under his authority....
Carltona principle is derived from this case – a civil servant may exercise a statutory power on behalf of a minister even though the statute does not expressly allow the minister to delegate such exercise.
Attorney-General v Jonathan Cape 
Claimant, the Attorney General, sought an injunction against the defendant, acting on behalf of deceased cabinet Minister Richard Crossman and the Sunday Times.
Crossman had kept a detailed diary documenting his time in the Cabinet during 1964 – 70. He wished to publish the diary in full to challenge the traditional secrecy of British Government and to give the public an insight into Government decision making. Crossman died before the diaries were published. After his death the Sunday Times began to print extracts and the executors of his will planned to publish the diaries in full, in accordance with Crossman's wishes.
The Attorney General argued the convention of collective Cabinet responsibility, which requires Ministers to support policy decisions of the Cabinet and not to disclose the attitude of individuals, was the issue. Further that the convention was enforceable by the courts on the grounds of public interest.
The defence contended that the convention is not a legal obligation which the courts can enforce, except in national security cases. Further that if publication of Cabinet proceedings was contrary to the public interest it should be stated in legislation.
The court decided not to enforce the convention of Cabinet secrecy by granting an injunction to prevent publication. It was held that in this case an injunction was unnecessary as the diaries could no longer be considered confidential, as ten years had passed.
However, the court acknowledged that in principle there is a legal obligation of confidentiality in relation to Cabinet proceedings.
Statute and Convention
Courts seem to be willing to acknowledge the existence of conventions. Conventions may indirectly give rise to legal obligations which the courts will enforce.
This means that conventions can be used in court to support arguments of law but cannot be used to contradict arguments of law. For example, if an Act of Parliament was passed which is in breach of a convention, it may be an unconstitutional Act but the courts will not necessarily recognise it as illegal and refuse to apply the Act.
Madzimbamuto v Lardner Burke 
The Privy Council was required to hear an appeal from the Rhodesian courts. The Privy Council had to decide whether Parliament could lawfully legislate for Southern Rhodesia after that country had declared its independence. The Government of Southern Rhodesia contended that there was a convention which required their consent before any UK legislation could apply to Southern Rhodesia.
.. It may be that it would be unconstitutional to disregard this convention. But it may also be that the unilateral Declaration of Independence released the United Kingdom from any obligation to observe the convention. Their Lordships in declaring the law are not concerned with these matters. They are concerned only with the legal powers of Parliament....
The case advocates the view that a convention has no legal effect in limiting the legislative power of Parliament.
Refusal to Enforce
There is judicial discretion in interpreting the law. Theoretically, this could enable courts to place more or less weight on constitutional conventions in some circumstances. However, it seems courts have resisted doing so.
The reasons for this may include the fact that conventions are formed by precedents set by institutions of Government not judiciary. It is important that there is no obligation for courts to enforce conventions and to do so would involve formal sanctions. Difficulties would arise from trying to resolve conflicts between laws and conventions. Essentially, if courts were to attempt to enforce constitutional conventions they would no longer be conventions or so distinct from laws.
It has been suggested that conventions should be written to try to make them less flexible and more explicit. However, this creates the possibility of conflict between the actual practice and the text of the convention. The Ministerial Code, first published in 1992, does go some way to enunciating the constitutional conventions in relation to Ministerial Responsibility.
The uncertainty of conventions can be criticised. However, their flexibility can be seen as an advantage especially in allowing for political development, for example in the relationship between Crown and Government. Legal certainty required to satisfy the concept of the rule of law can be seen as focussed on matters concerning individual liberty rather than constitutional mechanisms.
Enforcement by the courts has been raised as a possibility. However this would blur the separation of powers because it is the judiciary’s role to resolve legal disputes and for the executive to govern according to law. Conventions can be seen as political practices with the ability to evolve which would be altered completely if the courts became enforcer of constitutional conventions.