Some principles of constitutional law are also found in common law, i.e. the decisions of judges. Important rules of constitutional law can be found in many judicial decisions. In the case of Entick v Carrington it was determined that general search warrants were illegal and in M v Home Office the circumstances under which a minister could be held to have acted in contempt of court in his official capacity were considered. These decisions illustrate the key role that the judiciary plays in the development of constitutional law.
When it comes to the operation of Parliament, there are certain rules relating to the functions, procedure, privileges and immunities of each House. Some of these rules are found in resolutions of each House and others remain unwritten, being based solely on informal understandings or practise. The ordinary courts have no jurisdiction over the law of Parliament.
Many rules of the constitution are not contained in Acts of Parliament or judicial decisions (case law) but are to be found in rules of conduct called conventions. Conventions could be defined as rules of constitutional behaviour which are considered to be binding upon those who operate the constitution but which are not enforced by courts of law or by the presiding officers in the Houses of Parliament. Constitutional conventions serve to regulate key aspects of the workings of government.
They regulate the operation and powers of the executive, the legislature and the judiciary.
Conventions are obeyed because of the political difficulties which follow if they are not. More generally conventions are obeyed because the breach of those principles will most times bring the offender into conflict with the courts and the law of the land.
The basic distinction between law and convention is that when a rule is a rule of law, it is in general within the functions of courts to declare that the specific rule is broken. Therefore a legal rule is either formally expressed or illustrated by a decision of a court, whereas conventions arise out of practise.
Generally a rule of law has greater importance than a convention. It is more effective to say that someone has acted illegally rather than unconstitutionally.
Conventions provide a means of bringing constitutional change without the need for formal change of the law. They allow the constitution to evolve and keep up to date without the need for formal enactment or repeal of law. From the other hand the law can be rigid and difficult to change. Therefore this is why it is preferable not to give a convention any legal status.
Due to the fact that conventions are not legal rules, it is concluded that they cannot be enforced in a court of law. However in appropriate cases the court was able to recognise the existence of conventional rules when deciding certain points of law. Such cases are Liversidge v Anderson where the court recognized that a minister is responsible to the parliament for the exercise of power, and Attorney General v Jonathan Cape Ltd where it was inferred that injunction could be granted to protect Cabinet secrecy.
