Constitutional Statute Law consists of those Acts of Parliament that play a key role in defining the relationship between the government and the people or between different elements of government (Human Rights Act (1998) or Parliament Acts (1911 and 1949). Statute Law is the supreme source of the UK constitution. Under the doctrine of parliamentary sovereignty, the passing of a new statute can make or unmake any exisiting laws and overturn any other constitutional practice.
Common Law (often referred to as case law or 'judge-made law') refers to established customs customs and legal precedent developed through the actions of judges. Most of the traditional civil liberties available to UK citizens, including freedom of speech were originally established in common law. The royal prerogative (including the power to declare war and agree treaties) is also rooted in Common Law.
Conventions are traditions or customs that have evolved over time and have become accepted rules of behaviour. Conventions have no real legal standing. As a result, they can be easily overturned with the passing of a parliamentary statute. As conventions merely reflect accepted practice, they can also fall into disuse as practices change. The doctrine of cabinet collective responsibility is rooted in convention.
EU Laws and Treaties
Under the European Communities Act (1972), the UK incorporated the Treaty of Rome (1957) into their laws. This gave European Laws and treaties precedence over UK national laws. (Parliament obviously reserves the right to repeal the 1972 Act and subsequent treaties - and thereby withdraw from the EU).
Works of Authority
Works of authority are scholary texts which serve to codify practices not outlined on paper anywhere. These works have only a persuasive authority, the fact that many have been used as constitutional references for over 100 years awards them a certain status. Key texts include Erskine May's Parliamentary Practice (first published in 1844) and AV Dicey's An Introduction to the Study of the Law of the Constitution (1855).
Parliamentary Sovereignty - The doctrine of parliamentary sovereignty holds that the Westminster Parliament retains supreme political power within the UK system of government.
Royal Prerogrative - Consists of those powers traditionally exercised by the monarch. Many of these powers are now exercised by the prime minister on behalf of the monarch.
Collective Responsibility - The principle that as decisions are taken collectively within cabinet, cabinet memebers are expected to support those decisions made publicly - or resign their posts.