Uncodified British Constitution
The term constitution can be applied to any overall system of law that defines the functioning of a government. In an additional sense, it could be said that a constitution consists of a body of legal and political rules or arrangements that regulate the way in which the country operates, including the relationship between citizen and state.
Similarly, the House of Lords Select Committee on the Constitution defines a constitution as being “the set of laws, rules and practices that create the basic institutions of the state and its component and related parts, and stipulate the powers of those institutions and the relationship between the different institutions and between those institutions and the individual".  A constitution establishes the organs of government and traditionally, it consists of three main bodies. These bodies are effectively responsible for the legislative, executive and judicial functions within the country.
However, unlike most other countries, the United Kingdom does not have a core constitutional document that enshrines these rules and regulations as set out in the definition above. It is therefore referred to as an ‘uncodified’ constitution. Nonetheless, the UK’s constitution, although ‘uncodified’, still has written aspects to it. The majority of it is written in laws, statutes, legislation and more recently the European Union Law. It is for this reason that perhaps the term ‘uncodified’ is more appropriate than the term ‘unwritten’ when defining the constitution of the United Kingdom.
This is a characteristic which is not shared by many other nations namely, the United States of America  and the Republic of Ireland  . These countries have their rules and laws enshrined in a single written document and are codified. Codified constitutions are inflexible, therefore making the process by which the law is changed or introduced much more difficult than that of the UK. It has been argued that a common feature of written constitutions is the ‘constitutional law has status of higher form of law’  which can only be amended by special procedure. For example, in the ROI  , in order for any aspect of the constitution to be changed, a bill must be passed by both Parliaments, receive a majority of votes in the referendum and have the assent of the President. This is not the case for the UKs constitution as the legislation can be amended, enacted or repealed through Parliament. This is a key feature of our constitution and a main function of Parliament. As the US constitution is codified and is overt, clear-cut and moderately short, it is selected as the supreme law of the land. This differs to Britain’s constitution, which has many origins and forms. These include statutes, common law and conventions.
It could be said that perhaps the United States of America is less democratic than the UK in this respect, in view of the fact that if American citizens want a modification, they have to fight much harder to achieve it. In Ghaidan v Godin-Mendoza   , Baroness Hale states that “Democracy is founded on the principle that each individual has equal value … democracy values everybody equally, even if the majority does not".  The UK is often seen to be a liberal and democratic country with a commitment to freedoms. Liberty became a frequent feature of the British Constitution as far back as Magna Carta 1215 to the present day Human Rights Act 1998. Baroness Hale made the speech above in light of this vision.
The UK has a unitary system of Government, with political control concentrated at the core. Unlike the USA, it is undivided. In the US Constitution, state governments share responsibilities in certain areas to ensure the functioning of state-wide programs throughout the country.
Another key feature of the UKs constitution is Parliamentary Sovereignty or subordinate to the legislature. The legislature in the UK (and other countries that have an unwritten constitution)  is supreme. This principle was stated and applied in the case of Cheney v Conn   by Ungoed-Thomas J when he said “It is, I may add, the Queen in Parliament and not the Queen independently of Parliament, acting as the executive through the cabinet, who makes what is law in this land."  This principle was again re-iterated only in different terms, by Lord Steyn in the case of R v Attorney General .  ‘As the legislative powers of the state are unlimited’,  Parliament in Westminster can delegate its executive and legislative powers to other regions within the state,  giving them considerable self governance. This was granted through the devolution process in the Northern Ireland Act 1998. 
Referring to the earlier suggestion of a constitution comprising of three bodies,  the doctrine of the separation of powers is a fundamental concept in the United States constitution, supporting this. Montesquieu based his analysis of the Separation of Powers on the notion of the three distinct functions of government.  He believed that power should be vested equally between these three functions so that no one body has excessive power. Montesquieu also believed that “loss of intermediate powers made possible the revolutionary move from royal to popular tyranny".  This theory by Montesquieu was adopted by the authors of the United States Constitution as they intended to follow the doctrine by having a limited government. Each of the three bodies has its own function in the US Constitution and runs a ‘check and balance’  system. By doing so, they ‘exercise some control or check over the other two’.  The UK constitution doesn’t create this separation of powers; although the judiciary is mainly independent there are key connections between the executive and the legislature. Members of the executive are members of Parliament making them part of the legislative branch and so on. However, we do see evidence of the Separation of Powers in the British Constitution in the case of Duport Steels Ltd v Sirs  where Lord Diplock states “it cannot be too strongly emphasised that the British Constitution, though largely unwritten, is firmly based on the separation of powers: Parliament makes the laws, the judiciary interpret them." 
Amid the key features of the UK Constitution, there are sources upon which it is based and if it were not for these sources, we would not have a constitution.
Hilaire Barnett  splits the sources of the British Constitutional law into two Categories: Legal Sources  and Non Legal Sources. Statutes are the main source of the British Constitution and from as early as the 16th century, statutes established the Parliament, Roles of the Monarchy, Powers of the Houses of Lords and Commons and also the responsibilities of the judiciary. In the case of Thoburn v Sunderland City Council   , the court heard that there are two categories of statutes within the UK, Constitutional and Ordinary statutes. Ordinary statutes are subject to implied repeal whilst Constitutional Statutes are not. However, since the case, there has been great controversy regarding the existence of these ‘constitutional’ statutes. Some of the “constitutional" statues as discussed previously  include: Magna Carta 1215, The Bill of Rights 1688 to more recently, The European Communities Act 1972 (providing for the incorporation of EU law into the UKs domestic legal system) and The Human Rights Act 1998 (gives legal effect to the ECHR). The House of Lords Select Committee on the Constitution state that “The constitution is uncodified and although it is in part written there is no single, accepted and agreed list on statutes which form that part of the constitution which is indeed written down". 
In the case of Entick v Carrington   we see the importance of statute in case law where without legal authority and in the absence of a statute, the executive can do nothing.
Conventions are also classed as being a source of the constitution however these are not legally binding. Conventions are unwritten rules determining the conduct of government. Most of them arise out of the transfer of royal prerogative powers over the centuries to parliament and to ministers. Main examples of conventions operating within the British constitution include, that the Prime Minister has the power to appoint all government ministers and has the sole power to choose the dates of the general election. Dicey stated that constitutional conventions were ʺ…. rules for determining the mode in which the discretionary powers of the Crown ought to be exercised. … Conventions are constitutional rules, which are not laws in the strict sense..... which are designed to control the use of discretionary power by the Crown." 
In conclusion, the constitution of the United Kingdom can be seen to take a more ‘laid back’ approach when viewed alongside the constitution of the United States and Republic of Ireland. Perhaps this is due to the flexibility of our constitution. It could lead some to argue that the constitution should codified and better structured like the US, but with the continuous use of the various features such as the separation of powers, constitutional monarchy, parliamentary sovereignty and democracy, the British constitution is more than acceptable just the way it is.
A constitution is a plan that provides the rules for government. It serves several purposes; first, it sets out the ideals of the people; it establishes the basic structure of the government; it defines the powers and duties of the government; and it provides the supreme law for the nation. In the US the purpose of a constitution is both a grant of power from the States of the Union and a set of restrictions and prohibitions. It can be compared to a game in the sense that most games have rules. The Constitution for the US government is a document outlining and laying down these rules. They are created by the States to create the federal government.
In the UK however, the constitutions enables the government to provide clear leadership to the state and aid the active involvement of its citizens. The constitution is also in place to promote environmental, ecomomic and social well being. It could go as far as to enable decisions to be taken efficiently and effectively; create a powerful and effective means of holding decision-makers to account; ensure that no-one will review or scrutinise a decision in which they were
directly involved; ensure that those responsible for decision-making are clearly identifiable
to local people and that they explain the reasons for decisions; and provide a means of improving the delivery of services to the community.