Parliament is the only body which can make laws in the United Kingdom

In UK, therefore, statute law has precedence over the other sources of the unwritten constitution. However, the principle if parliamentary sovereignty cannot be found in any Act of Parliament. It is a part of common law which established itself as judicial rule in the late 17th century, following the 'Glorious Revolution' of 1608. Parliamentary sovereignty implies that parliament can pass, adopt or repeal any law it likes and it is not bound by any other previous parliaments' laws.

There are several arguments applicable to the context of the constitution of the United Kingdom; the effect of the UK constitution not being composed of written or codified rules, the doctrine of rule of law as put forward by Professor Albert Venn Dicey in ‘The Law of the Constitution’1 and the  parliamentary sovereignty.

The UK constitution is comprised of unwritten conventions and rules, though the Bill of Rights 1689 has provided the basis for the legislative powers of Parliament and common law for the powers of the Monarch. Dicey was of the view that the UK constitution, although being unwritten, was based upon the principles of the legal sovereignty of Parliament and the rule or supremacy of law2. 

Dicey’s view was that the rule of law stated that firstly, individuals could not be subject to a wide discretionary legislative power, that everyone would have the same fair treatment in the courts, and that as there was no written constitution, that constitutional law was the “result of the judicial decisions determining the rights of private persons in particular cases brought before the courts".

The United Kingdom does not have a codified constitution, unlike France or the United States, and this has a historical basis.  From the end of the eighteenth century and throughout the nineteenth century there was a push towards the principle of constitutionalism, that there should be limits upon the absolute power of government, as it was recognised that this was very dangerous if unchecked, and the revolution in France in 1789 and 1830, the appointment of an absolute monarch in Spain in 1812 and the establishment of the constitution of the Kingdom of Italy are examples of the wave that occurred at this time.

1 http://www.constitution.org/cmt/avd/law_con.htm

2 http://everything2.com/title/Dicey%2527s+views+on+the+rule+of+law+and+the+supremacy+of+parliament .

In the context of parliamentary sovereignty (Parliament in the UK being the supreme and absolute power) which has long been accepted as the fundamental doctrine of constitutional law in the UK, the purpose of a constitution is to limit such powers of government and divide powers amongst different bodies with a view to establishing a check on those powers, called the separation of powers

In the eighteenth century, there was a balance of powers of the King, House of Lords and the House of Commons in the United Kingdom, and at the time that Dicey advocated his views about the constitution, this balance of power was followed more avidly than in the present day, as the Monarch had considerable discretion to choose the Prime Minister, and the House of Lords had the same powers as regards participating in making of legislation as the House of Commons.  The Preamble to the Parliament Act 1911 removed the House of Lord’s power to veto legislation passed by the House of Commons, and since thereafter there has been no constitutional mechanism by which the House of Common’s supremacy can be challenged.

The UK's constitution is not written in a single document, but derives from a number of sources that are part written and part unwritten, including accumulated conventions, works of authority, Acts of Parliament, the common law, and EU law.

Historically, the UK has not had a definable statement of individual rights and freedoms either - the 1689 Bill of Rights sets out the powers of parliament verses the monarch - but rather relies on the notion of residual freedom and the concept of parliamentary sovereignty.

Therefore, individuals' rights remained dependent on ad-hoc statutory protection or upon judicial protection under common law. This contrasts to many European and Commonwealth countries and the United States, which have a clearly defined constitutional settlement. The closest thing the UK has to a bill of rights today is the Human Rights Act 1998, which incorporates the European Convention of Human Rights 1950 (ECHR) into domestic law.

The UK, despite not possessing a formal written constitution, has a series of notable constitutional documents. These begin with Magna Carta3, written in 1215, which outlined some important principles curbing the arbitrary rule of the monarch. This document, while not of legal relevance today, has important symbolic value for establishing the rights of citizens and limiting legislative power. Magna Carta was followed by the Bill of Rights 16894, which extended the power of Parliament, and then by the Reform Act 1832, which began the process of democratising British politics. The entry of the UK into the European Union in 1973 was a major constitutional development, bringing Britain under the supra-national jurisdiction of the EU in a limited number of areas, which have grown in the following years. The Factortame case5 of 1990 (involving the denial of UK fishing rights claims) illustrated the erosion of the UK's unfettered sovereignty. The incorporation of the European Convention on Human Rights into UK law by the Human Rights Act 1998 provided individuals with the ability to bring claims in domestic courts based on these prescribed human rights. The Act is of major constitutional significance because it strengthens the ability of ordinary people to challenge the actions of the various institutions of government. Britain ratified the European Convention on Human Rights in 1951, and since 1955 has accepted the right of individual petition to the European Commission on Human Rights, thus making EU law a source of the UK Constitution.

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3 http://www.independent.co.uk/news/uk/politics/the-big-question-why-doesnt-the-uk-have-a-written-constitution-and-does-it-matter-781975.html

4 http://en.wikipedia.org/wiki/Bill_of_Rights_1689

5 http://www.oup.com/uk/orc/bin/9780199544455/resources/updates/factortamecase.pdf

Another criticism of the UK un-codified Constitution is that the current government with its overwhelming majority can potentially change the Constitution by implementing new laws over-riding previous laws as stated in Dicey’s Rule of Law (Parliament being able to make and un-make laws). As a result of elective dictatorship which Lord Hailsham (Lord Chancellor 1970-74) said, power had centralised itself more and more in the House of Commons, more on the government side of the House, and more on the front benches. The House of Lords was not an effective balancing factor except in rare cases and its influence on government was far weaker than that of second chambers in other countries e.g. the USA. This is relevant as it leads back to the ability of the government with it’s overwhelm.

Many people argue that the UK needs a written constitution in order to restrain the unbridled power of the executive. However, with the executive located in and dominating parliament, anything that limits the power of the government undermines the traditional doctrine of parliamentary sovereignty. A written constitution, in particular, would refute the convention that no future government can be bound irrevocably by the actions of a former government.

As such, the core controversy around the notion of a written constitution has been its potential to act as a brake on the democratic supremacy of parliament. Some believe that the notion of an unelected judicial branch questioning the sovereignty of parliament is fundamentally opposed to the notion of representative democracy.

This is where the 1998 Human Rights Act struck an interesting and delicate compromise.

By only investing the judiciary with the power to make a declaration of incompatibility, and by making it clear that parliament only had a duty to 'consider' this, the government managed to invest the judiciary and public with a new rights-based settlement, but also succeeded in retaining the principle of parliamentary sovereignty.

Unlike the 'special' constitutional law that a written constitution would entail, the HRA has no special status, and is simply a statute with the same force as any other, but with a universal scope. In theory, it could be repealed with no special procedure - although the UK would continue to be bound by its international obligations under the European Convention on Human Rights.

Many critics of the measure claimed that the 1998 Human Rights Act would lead to the collapse of the public sector with each and every aggrieved individual relying on indefinable rights to challenge decisions that went against them. This 'floodgates' fear failed to materialise in the years since the introduction of the Act but there were concerns about the interpretation of the act, for example in the criminal justice system, where critics argued the law was being used to protect offenders more than victims.

http://www.independent.co.uk/news/uk/politics/the-big-question-why-doesnt-the-uk-have-a-written-constitution-and-does-it-matter-781975.html?action=Popup