The British constitution has evolved over many centuries. Unlike the constitutions of America, France and many Commonwealth countries, the British constitution has not been assembled at any time into a single, consolidated document. Instead it is made up of common law, statute law and convention.

Although it does not have a single document codifying the way its political institutions function and setting out the basic rights and duties of its citizens, Britain does have certain important constitutional documents. These include the Magna Carta (1215) which protects the rights of the community against the Crown; the Bill of Rights (1689) which extended the powers of Parliament; and the Reform Act (1832) which reformed the system of parliamentary representation.

Common law has never been precisely defined – it is deduced from custom or legal precedents and interpreted in court cases by judges. Conventions are rules and practices which are not legally enforceable, but which are regarded as indispensable to the working of the government. Many conventions are derived from the historical events through which the British system of government has evolved. One convention is that Government Ministers are responsible and can be held accountable for what happens in their departments.

The flexibility of the British constitution helps to explain why it has developed so fully over the years. However, since Britain joined the European Community in 1973, the rulings of the European Court of Justice have increasingly determined and codified sections of British law in those areas covered by the various treaties to which Britain is a party. In the process, British constitutional and legal arrangements are begining to resemble those of Europe.