Professor King states, “A constitution is the set of rules that regulate the relations among the different parts of the government of a given country and also the relations between the different parts of the government and the people of the country". 
Colin Turpin suggests that the constitution is: “a body of rules, conventions and practices which regulate or qualify the organization and operation of government in the United Kingdom’ deSmith’s classic introductory text regards the constitution as ‘a central, but not the sole feature, of the rules regulating the system of government’  .
A slightly longer version is offered by Vernon Bogdanor, for whom the constitution is: ‘a code of rules which aspire to regulate the allocations of functions, powers and duties among the various agencies and officers of government and defines the relationship between these and the public’. 
Characteristics of the UK constitution: The first one is written or unwritten constitution. A Lot of people think the written constitution is better than the unwritten constitution. As example human rights are inalienable. This means that human rights cannot be taken away from a person. As a result of that written constitution is like an insurance for people whose rights have being breached by the government. As opposed to an unwritten constitution which is not contained in a codified document, therefore the rights of the citizens and remedies for breach of those rights are not written down. Consequently people are left unsafe.
The next characteristic of constitution is; flexible or inflexibility. If the country has a flexible constitution they can fulfill their needs easily. Hence the procedure for amendments of the constitution is less as opposed to an inflexible constitution, where the need for a special majority and referendum need to take place.
The third characteristic of the constitution is; monarchical or republican. Monarchical is where the Queen is head of the state. As opposed to a republican constitution where the powers of the Queen are somewhat limited and the head of the state is the president.
The parliamentary or presidential characteristic of the constitution is the next type of constitution. Prime minister is the head of parliamentary system and in the presidential system president is the head of the country.
The last characteristic of the constitution is; federal or unitary constitution. Under a unitary constitution all the powers are wasted to central government and under the federal constitution there is a separation of powers.
In considering the history of the UK constitution, Magna Carta is one of the documents in the history of UK constitution. It is established in 1215 and it is the first document that included human rights in the UK. After that as a result of Darnel’s Case 1627 (the Five Knights’ Case)  the Petition of Right was established in 1628 and then “The Bill of rights 1689 is of greater contemporary constitutional importance than the Magna Carta and the Petition of Right".  There by considering the above facts, it is clear that UK has a constitution appears as a partly written down constitution.
“The British Constitution refers to the principles, procedures, and precedents that governed the operation of the British government. These could be found in no single written document, however; Parliament and the King made the Constitution by their actions". 
The sources of UK constitution are Acts of parliament, case law and EU law. The UK has a constitution even though there is no one written document. So it’s an unwritten constitution. But principals are clearly written in some documents. As an example the UK government refers to these documents for their constitution.
- Magna Carta 1215
-Bill of Rights 1685
- Act of Settlement 1707
- Parliament Act 19141/1945
- Human Rights Act 1998
These documents are clearly said that UK constitution is not a 100% unwritten constitution.
The UK constitution has lot of advantages and disadvantages. In comparing the American constitution, UK constitution is an unwritten constitution and the USA constitution is a written one.“Written constitutions are valuable in the sense that they provide some indication of what actually in happens in practice".  If you can change the constitution with a simple majority it’s a flexible constitution. “The UK constitution tends to be regarded as a flexible constitution in that it can be amended simply by passing an Act of parliament: there is no special procedure to be followed".  It’s proved that the UK constitution is flexible constitution.
In the 19th century, A.V. Dicey wrote the "twin pillars" of the British constitution. The first pillar is the principle of Parliamentary sovereignty and the second one is the rule of law. If we giving attention to the Sovereignty of parliament. Supreme to all other government institutions means the sovereignty and its implies that the legislative body may change or repeal any prior legislative acts.UK also parliamentary sovereignty is the most important part of their constitution because the Parliamentary sovereignty is a principle of the UK constitution. Parliament is the highest source of British law.
Parliament can make law about anything in the country. And also current parliament does not bound it predictors. Parliament is the supreme lawmaker and the court can’t ask questions from parliament about their works. In the Madzimbamuto v Lardner-Burke,  Lord Reid states,
“It is often said that it would be unconstitutional for the United Kingdom Parliament to do certain things, meaning that the moral, political and other reasons against doing them are so strong that most people would regard it as highly improper if Parliament did these things. But that does not mean that it is beyond the power of Parliament to do such things. If Parliament chose to do any of them, the courts would not hold the Act of Parliament invalid".
It’s proved that parliament sovereignty is the most powerful thing in the country.
In A.V. Dicey’s view, parliamentary sovereignty entails three principal aspects:
Parliament has the power to another or change any law what so ever.
No Parliament can be restricted by a predecessor or bound its successor.
Nobody, including the court, may question the validity of Acts of Parliament.
“Lord Reid’s remarks in Madzimbamuto represent a classical formulation of the traditional view that there are no legal limits on the legislative power of parliament. Parliament has the power to make whatever laws it thinks fit, including repressive laws of the most barbarous kind. Thus to take an example deployed by Leslie Stephen, Parliament could, if it so wished, enact a law that all blue-eyed babies should be killed birth". 
This shows that supreme power of parliament Sovereignty. Parliament can do anything as they wish, but “In practice, therefore, there is a clear distinction between what Parliament can do and what it will do".  But this has limited to a certain extend. However the parliament sovereignty is the most powerful thing in the UK.
If we give attention to the judicial obedience to Act of Parliament, in the case of Ex p Canon Selwyn (1872)  its raised the question of the validity of the monarch. The Irish Church Disestablishment Act 1869, Cockburn CJ stated that: “There is no judicial body in the country by which the validity of an Act of Parliament could be questioned. An Act of the legislative is superior in authority to any court of law. We have only to administer the law as we find it, and no court could pronounce a judgment as to the validity of an Act of Parliament." 
In the case of Madzibamuto v Lardner-Burke (1969) 
“Lord Reid stated that: It is often said that it would be unconstitutional for the United Kingdom Parliament to do certain things, meaning that the moral, political and other reasons against doing them are so strong that most people would regard it as highly improper if Parliament did these things. But that does not mean that it is beyond the power of Parliament to do such things. If Parliament chose to do any of them the courts could not hold the Act of Parliament invalid." 
And there are some incidents where the Parliament has acted in the same manner. In Burmah Oil v Lord Advocate  , Burmah oil failed to obtain their compensation, because the judicial decision can’t overcome to sovereignty of Parliament. These examples are proving that the parliament of sovereignty is the highest power in the UK rather than judicial obedience.
If we give attention to the limitation of sovereignty, even though Parliament sovereignty is the principal characteristics of the British constitution it can be limited in some circumstances. Those are European Law, Devolution of powers, the manner and form argument and European Court of Human Rights.
European Communities Act 1972 provides that “any enactment passed or to be passed… shall be construed and have effect subject to the foregoing provisions of this section"  . It proves that European Community can limit the parliament sovereignty in UK.
Devolution of powers mean Wales, Scotland and Northern Ireland can make their own laws as they wish. V. Bogador states that devolution has three parts,
1. The transfer of power to a subordinate elected body
2. The transfer of power on a geographical basis
3. The transfer of functions at present exercised by Parliament 
These three parts notice that devolution of powers also limit the parliamentary sovereignty in UK.
Professors Heuston and Marshall including the view of manner and form that “whilst there are no limits on the subject matter upon which Parliament may legislate, the manner and form in which Parliament may be circumscribed"  . It proves that the manner and form argument also can limit the Parliament sovereignty.
If we give attention to the European Court of Human Rights, there was case named Gillan and Quinton v the UK. The two parties appeal to the House of Lords but the House of Lords dismissed their appeal as the section44 the terrorism Act the police acted in an authority way. However the UK government response were that under the section 44 the police can use their powers further these powers will be used under specific occasions. Therefore the UK government is not bound by the ECHR decision and the Act of Parliament cannot challenge it.