English law, the law of England and Wales (but not Scotland and Northern Ireland) is considered by some to be one of Britain's great gifts to the world. Also known generally as the common law (as opposed to civil law), it was exported to Commonwealth countries while the British Empire was established and maintained, and persisted after the British withdrew or were expelled, to form the basis of the jurisprudence of many of those countries. Actually part of the English legal system has always been considered to be based upon the civil law, namely the ecclesiastical courts and the courts of admiralty.
The essence of common law is that it is made by judges sitting in courts, applying their common sense and knowledge of legal precedent to the fact before them. Because common law consisted of using what had gone before as a guide, common law places great emphasis on precedents. Thus a decision of the highest court in England and Wales, the House of Lords (the judicial members of which are referred to as Law Lords) is binding on every other court in the hierarchy, and they will follow its directions.
Precedent continues to be applied across both civil and criminal law to this day (as in other jurisdictions) allowing for decisions made in one Court regarding a set of facts and their interpretation in law to be applied to like circumstances in the future.
It is also for this reason that there is no Act of Parliament (the normal method for creating laws in the UK) making murder illegal. It is still a common law crime - so although there is no written Act passed by Parliament making murder illegal, it is illegal by virtue of the constitutional authority of the courts and their previous decisions. Common law can be amended or repealed by Parliament, for example, murder carries a mandatory life sentence today, but had previously allowed the death penalty.
However, while England and Wales retains the common law the UK is part of the European Union and European Union Law is effective in the UK. The European Union consists mainly of countries which use civil law and so the civil law system is also in England in this form, and the European Court of Justice, a predominantly civil law court, can direct UK courts on the meaning of EU law.
The oldest law currently in force is the Distress Act, 1267, part of the Statute of Marlborough, (52 Hen. 3). Three sections of Magna Carta, originally signed in 1215 and a landmark in the development of English law, are still extant, but they date to the reissuing of the law in 1297.