A high degree of centralization characterizes the UK's governing structure. Power is concentrated in Parliament, the national legislature. Since 1999, however, some legislative powers have shifted to a Scottish Parliament, a Welsh Assembly, and a Northern Ireland Assembly.
While further decentralization of the governing structure is likely, given that England accounts for 85% of UK's population, attainment of a fully federal system will be difficult to achieve.
Tabs to the right provide information on the three components of the UK government.
Parliament consists of two chambers. The House of Commons is the elected lower chamber. The unelected upper chamber is the House of Lords.
The right to sit in the House of Lords was at one time restricted to those who held hereditary titles. In current times, members of the House of Lords are appointed by Queen Elizabeth II, with advice from the prime minister and an independent commission.
Either chamber may introduce a bill, also called Draft legislation, although revenue bills must originate in the House of Commons.
Bills proceeds through a multi-step legislative process, as pictured below.
Both chambers must approve a bill in the same form before it can receive the Royal Assent and become a legally binding Act of Parliament.
For more detailed information on this process, see How a Bill Becomes Law.
Image source: UK Parliament website.
A cabinet-style government wields executive power at the national level in the UK. 
This cabinet is formed by the party (or coalition of parties) that attains a majority in the House of Commons.
The Prime Minister is the head of the national government, and leads the majority part in the House of Commons. Other members of the cabinet as well as sub-cabinet officials, are known as ministers. They are appointed by the Prime Minister.
These ministers are usually members of the House of Commons, and are also usually affiliated with the same political party. Members of the House of Lords, however, may also serve as ministers.
The national government exercises its authority in the name of a hereditary monarch. The current monarch is Queen Elizabeth II. She serves as the head of state, although her role is largely ceremonial.
Image Source: 10 Downing Street, Flikr, CC BY 2.0.
The UK does not have a single unified court system.
Scotland and Northern Ireland have their own individual judicial systems. Northern Ireland's court system closely resembles that of England and Wales. The Scottish court system combines elements of common law and civil law systems.
England and Wales share a unified court system which originated in medieval England and is based on common law principles.
In England and Wales, most civil cases are heard in the County Court. Specialist tribunals resolve particular types of civil disputes, such as those involving taxation and employment, immigration and asylum cases.
Criminal cases are heard in the Magistrates' Court, with the Crown Court hearing more serious offenses.
The High Court functions as both a court of first instance for high value civil claims and as an appellate court for civil and criminal cases. It consists of three divisions: the Queen's Bench, the Chancery Division, and the Family Division.
Functioning as an appellate chamber is the Court of Appeals. The Civil Division hears appeals form the High Court and the County Court, and the Criminal Division hears appeals from the Crown Court.
The Supreme Court sits at the apex of the UK’s legal system. It hears appeals from courts in England and Wales, Scotland and Northern Ireland.
Image Source: Courts & Tribunals Website