The United Kingdom does not have a single legal system since it was created by the political union of previously independent countries, with Article 19 of the Treaty of Union guaranteeing the continued existence of Scotland's separate legal system. Today the UK has three distinct systems of law: English law, Northern Ireland law and Scots law. Recent constitutional changes saw a new Supreme Court of the United Kingdom come into being in October 2009 to replace the Appellate Committee of the House of Lords.The Judicial Committee of the Privy Council, including the same members as the Supreme Court, is the highest court of appeal for several independent Commonwealth countries, the UK overseas territories, and the British crown dependencies.
Both English law, which applies in England and Wales, and Northern Ireland law are based on common-law principles. The essence of common law is that, subject to statute, the law is developed by judges in court, applying statute, precedent and common sense to the facts before them, to give explanatory judgements of the relevant legal principles, which are reported and binding in future similar cases (stare decisis). The courts of England and Wales are headed by the Senior Courts of England and Wales, consisting of the Court of Appeal, the High Court of Justice (for civil cases) and the Crown Court (for criminal cases). The Supreme Court is the highest court in the land for both criminal and civil appeal cases in England, Wales, and Northern Ireland and any decision it makes is binding on every other court in the same jurisdiction, and often has a persuasive effect in other jurisdictions.
Scots law, a hybrid system based on both common-law and civil-law principles, applies in Scotland. The chief courts are the Court of Session, for civil cases, and the High Court of Justiciary, for criminal cases. The Supreme Court of the United Kingdom serves as the highest court of appeal for civil cases under Scots law. Sheriff courts deal with most civil and criminal cases including conducting criminal trials with a jury, known as sheriff solemn court, or with a sheriff and no jury, known as sheriff summary Court. The Scots legal system is unique in having three possible verdicts for a criminal trial: "guilty", "not guilty" and "not proven". Both "not guilty" and "not proven" result in an acquittal with no possibility of retrial.
Crime in England and Wales increased in the period between 1981 and 1995, though since that peak there has been an overall fall of 48% in crime from 1995 to 2007/08, according to crime statistics. The prison population of England and Wales has almost doubled over the same period, to over 80,000, giving England and Wales the highest rate of incarceration in Western Europe at 147 per 100,000. Her Majesty's Prison Service, which reports to the Ministry of Justice, manages most of the prisons within England and Wales. Crime in Scotland fell to its lowest recorded level for 32 years crime in 2009/10, falling by ten percent in the last year. At the same time, Scotland's prison population, at over 8,000, is hitting record levels and is well above design capacity. The Scottish Prison Service, which reports to the Cabinet Secretary for Justice, manages Scotland's prisons. In 2006 a report by the Surveillance Studies Network found that the UK had the highest level of mass surveillance among industrialised western nations.