1. STATUTE LAW:

Law created by Parliament. Acts of Parliament must be approved by House of Commons, House of Lords and monarch before placed on statute book, i,e, gain force of law. Then are implemented by executive and enforced by courts. 

Acts of Parliament with constitutional significance (Examples of statute law):

• Great Reform Act (1832) = extended franchise
• Parliament Act (1911) = established House of Commons as dominant chamber in Parliament
• European Communities Act (1972) = UK joined European Economic Community (now the EU)
• Scotland Act (1998) = creation of Scottish Parliament -> (when power is given out away from Westminister = Devolution)
• Human Rights Act (1998) = enshrining key rights in UK law
• House of Lords Act (1999) = removing most hereditary peers from upper chamber

Statute law is most important source of principles and rules making up UK constitution. This is because, under doctrine of parliamentary sovereignty, parliament is supreme law-making body in UK. BUT it also means that parliament can amend or repeal any existing Act, so post-1997 Labour government was able to push through programme of constitutional reform. 

2. COMMON LAW

Legal principles that are developed and applied by UK courts. They interpret and clarify law where there is no clear statute law. Judicial decisions clarify rights of citizens against the state. These rulings then become part of body of common law, take precedence over previous rulings and serve as guide to future decision-makers. But ministers can seek to clarify or amend common law through Acts of Parliament.

Common law also includes customs and precedents that are accepted practice. These relate to role of monarchy, parliament and executive. Of major importance is royal prerogative (which is powers exercised in the name of the Crown) such as the power to:

• declare war and negotiate treaties
• dissolve parliament
• appoint government ministers
• appoint judges 

However, these powers do not still rest with the monarch, rather the PM.

3. CONVENTIONS

These are rules or norms that are considered binding. Long usage gives conventions their authority - they are neither codified nor enforced by courts of law. UK constitution is regarded as flexible because of some of key components such as those dealing with monarchy, are based on convention. 

Examples: 

• by convention, monarch must assent to Acts of Parliament
• monarch must accept advice of ministers on making treaties or declaring war
• monarch appoints PM but convention dictates that PM is leader of party in House of Commons with largest majority after general election
• last member of House of Lords to become PM was Alec Douglas-Home in 1963. By that time, convention dictated that PM should be in House of Commons, so he resigned from Lords and successfully fought by-election to take seat in House of Commons.
• in case of hung parliament, monarch faces big decision. After February 1974 general election, defeated PM Edward Heath explored possibility of forming coalition government with Liberals. Only when Heath admitted defeat was Labour's Harold Wilson as leader of minority party, invited to form minority Labour government.

4. AUTHORITATIVE WORKS

A number of established legal and political texts have become accepted as works of authority in UK constitution. They have no formal authority but are helpful in interpreting more obscure areas of constitutional practice. They act as a guide. 

Examples:

• Erskine May's Treatise on the Law, Privileges, Proceedings and Usage of Parliament (1844)
• AV Dicey's An Introduction to the study of the law of the constitution )1884)

5. EUROPEAN UNION LAW

On 1st January, 1973, the UK became a member of the European Economic Community (EEC). The EEC was renamed the European Community (EC) and since Maastricht Treaty came into force in 1993, was renamed the European Union (EU).

The treaties establishing the European Union, legislation emanating from the EU and judgements of the European Court of Justice have all become a part of the UK constitution.