England's most authoritative law is statutory legislation, which comprises Acts of Parliament, Regulations and Bye-Laws. In the absence of any statutory law, the common law with its principle of stare decisis forms the residual source of law, based on judicial decisions, custom, and usage. Its essence is that it is made by sitting judges applying both statutory law and the body of common law principles which have been established over the years from the reasoning of decisions in previous legal cases. A decision of the Supreme Court of the United Kingdom, the highest civil appeal court of the United Kingdom, is binding on every other court. Equity is a further source of judge-made law.
International treaties such as the European Union's Treaty of Rome or the Hague-Visby Rules have effect in English law only when adopted and ratified by Act of Parliament. Adopted treaties may be subsequently denounced by executive action.
Not being a civil law system, English law has no comprehensive codification. However, most of its criminal law has been codified from its common law origins, in the interests both of certainty and of ease of prosecution. For the time being, murder remains a common law crime rather than a statutory offence. Common law can be amended or repealed by Parliament; for example section 4 of the Carriage of Goods by Sea Act 1992 effectively overrules Grant v Norway.
Following Montesquieu's theory of the "separation of powers", only Parliament has the power to legislate; but in the event of a statute being ambiguous, only the courts have the power to decide its true meaning, using the principles of statutory interpretation. The courts have no authority to legislate, so the "legal fiction" is that they "declare" (rather than "create") the common law. The House of Lords took this "declaratory power" a stage further in DPP v Shaw, where, in creating the new crime of "conspiracy to corrupt public morals", Viscount Simonds claimed the court had a "residual power to protect the moral welfare of the state".
Although Scotland and Northern Ireland form part of the United Kingdom, they have separate legal systems, although they share Westminster as a primary legislature, and Supreme Court decisions of any UK country is binding on the others, as in Donoghue v Stevenson.  Even though Scotland became part of the UK over 300 years ago, Scots law has remained remarkably distinct from English law.
The first schedule of the Interpretation Act 1978, defines the following terms: "British Islands", "England", and "United Kingdom". The use of the term "British Isles" is virtually obsolete in statutes and, when it does appear, it is taken to be synonymous with "British Islands". For interpretation purposes, England includes a number of specified elements:
"Great Britain" means England, Wales, Scotland, their adjacent territorial waters and the islands of Orkney and Shetland, the Hebrides and, by virtue of the Island of Rockall Act 1972, Rockall. "United Kingdom" means Great Britain and Northern Ireland and their adjacent territorial waters, but not the Isle of Man, nor the Channel Islands, whose independent status was discussed in Rover International Ltd. v Canon Film Sales Ltd. (1987) 1 WLR 1597 and Chloride Industrial Batteries Ltd. v F. & W. Freight Ltd. (1989) 1 WLR 823. "British Islands" - but not "British Isles" - means the United Kingdom, the Isle of Man and the Channel Islands.
This became the usual way to refer to Acts in the second half of the 19th century, starting in the 1840s; previously Acts were referred to by their long title together with the regnal year of the parliamentary session in which they received Royal Assent, and the chapter number. For example, the Pleading in English Act 1362 was referred to as 36 Edw. III c. 15, meaning "36th year of the reign of Edward III, chapter 15", though in the past this was all spelt out, together with the long title.
Common law is a term with historical origins in the legal system of England. It denotes, in the first place, the judge-made law that developed from the early Middle Ages as described in a work published at the end of the 19th century, The History of English Law before the Time of Edward I, in which Pollock and Maitland expanded the work of Coke (17th century) and Blackstone (18th century). Specifically, the law developed in England's Court of Common Pleas and other common law courts, which became also the law of the colonies settled initially under the crown of England or, later, of the United Kingdom, in North America and elsewhere; and this law as further developed after those courts in England were reorganised by the Supreme Court of Judicature Acts passed in the 1870s, and developed independently, in the legal systems of the United States and other jurisdictions, after their independence from the United Kingdom, before and after the 1870s. The term is used, in the second place, to denote the law developed by those courts, in the same periods (pre-colonial, colonial and post-colonial), as distinct from within the jurisdiction, or former jurisdiction, of other courts in England: the Court of Chancery, the ecclesiastical courts, and the Admiralty court.
In the Oxford English Dictionary (1933) "common law" is described as "The unwritten law of England, administered by the King's courts, which purports to be derived from ancient usage, and is embodied in the older commentaries and the reports of abridged cases", as opposed, in that sense, to statute law, and as distinguished from the equity administered by the Chancery and similar courts, and from other systems such as ecclesiasical law, and admiralty law. For usage in the United States the description is "the body of legal doctrine which is the foundation of the law administered in all states settled from England, and those formed by later settlement or division from them".
Since 1189, English law has been described as a common law rather than a civil law system; in other words, no comprehensive codification of the law has taken place and judicial precedents are binding as opposed to persuasive. This may be a legacy of the Norman conquest of England, when a number of legal concepts and institutions from Norman law were introduced to England. In the early centuries of English common law, the justices and judges were responsible for adapting the system of writs to meet everyday needs, applying a mixture of precedent and common sense to build up a body of internally consistent law. An example is the Law Merchant derived from the "Pie-Powder" Courts, named from a corruption of the French pieds-poudrés ("dusty feet") implying ad hoc marketplace courts. As the Parliament of England became ever more established and influential, legislation gradually overtook judicial law-making such that today, judges are only able to innovate in certain very narrowly defined areas.
One of the major challenges in the early centuries was to produce a system that was certain in its operation and predictable in its outcomes. Too many judges were either partial or incompetent, acquiring their positions only by virtue of their rank in society. Thus, a standardised procedure slowly emerged, based on a system termed stare decisis which roughly means "let the decision stand". The doctrine of precedent which requires similar cases to be adjudicated in a like manner, falls under the principle of stare decisis. Thus, the ratio decidendi (reason for decision) of each case will bind future cases on the same generic set of facts both horizontally and vertically in the court structure. The highest appellate court in the UK is the Supreme Court of the United Kingdom and its decisions are binding on every other court in the hierarchy which are obliged to apply its rulings as the law of the land. The Court of Appeal binds the lower courts, and so on.
The influences are two-way.
Unlike Scotland and Northern Ireland, Wales is not a separate jurisdiction within the United Kingdom. The customary laws of Wales within the Kingdom of England were abolished by King Henry VIII's Laws in Wales Acts which brought Wales into legal conformity with England. While Wales now has a devolved Assembly, any legislation which that Assembly passes is enacted in particular circumscribed policy areas defined by the Government of Wales Act 2006, other legislation of the British Parliament, or by Orders in Council given under the authority of the 2006 Act.
Between 1746 and 1967, any reference to England in legislation was deemed to include Wales. This ceased with the enactment of the Welsh Language Act 1967 and the jurisdiction is now commonly referred to as "England and Wales". Although devolution has accorded some degree of political autonomy to Wales in the National Assembly for Wales, it did not have the ability to pass primary legislation until the Government of Wales Act 2006 came into force after the 2007 Welsh general election. That said, the Welsh legal system remains English common law, in that the legal system administered through both civil and criminal courts remains unified throughout England and Wales. This is different from the situation of Northern Ireland, for example, which did not cease to be a distinct jurisdiction when its legislature was suspended (see Northern Ireland (Temporary Provisions) Act 1972). A major difference is also the use of the Welsh language, as laws concerning it apply in Wales and not in the rest of the United Kingdom. The Welsh Language Act 1993 is an Act of the Parliament of the United Kingdom, which put the Welsh language on an equal footing with the English language in Wales with regard to the public sector. Welsh may also be spoken in Welsh courts.
English criminal law derives its main principles from the common law. The main elements of a crime are the actus reus (doing something which is criminally prohibited) and a mens rea (having the requisite criminal state of mind, usually intention or recklessness). A prosecutor must show that a person has caused the offensive conduct, or that the culprit had some pre-existing duty to take steps to avoid a criminal consequence. The types of different crimes range from those well known ones like manslaughter, murder, theft and robbery to a plethora of regulatory and statutory offences. It is estimated that in the UK, there are 3,500 classes of criminal offence. Certain defences may exist to crimes, which include self-defence, intention, necessity, duress, and in the case of a murder charge, under the Homicide Act 1957, diminished responsibility, provocation and, in very rare cases, survival of a suicide pact. It has often been suggested that England and Wales should codify its criminal law in an English Criminal Code, but there has been no overwhelming support for this in the past.
Chief Justice Coke's rulings in