Every organisation needs a constitution to define the powers, rights and duties and therefore it can be said that a constitution looks to both internal and external regulation of the body to which it relates. Under the United Kingdom's constitution, the manner in which constitutional change is effected will be depended not upon clearly written rules but, rather by accepted constitutional practice which Every organisation needs a constitution to define the has evolved over time.
A Constitutional and legal fact is that Parliament has the ultimate Law making power within the state but it does not mean that there are no restraints on what parliament may do. Parliament is accountable to the electorates, and the economic and political necessities. To study the British Constitution there must be an understanding of historical, legal, philosophical matters which over the centuries have shaped the organisation of the state.
It's almost unique in not having a written constitution and it's the product of many centuries of continuous and mostly gradual and peaceful evolution. It also has an unbroken history development dating from 1066. It is also necessary to understand issues such as, the conventions as a recognised source of the British Constitution. Constitutional conventions may not have a legal force, except those which have been given effect by statute (for instance, the Parliament Acts 1911-49, but someone can say that convention are as much, or even more important than legal rules.
There is not a clear definition of what are the British constitution conventions are but it can be said that they regulate in particular the exercise of the Royal Prerogative, the workings of the Cabinet system, the proceedings of Parliament including relations between the two Houses, the independence of the judiciary and the framework within which the Civil Service operates. After realising the importance of conventions it could be said that people should take them seriously and have in mind that breaching a convention may not be a breach of a legal rule but it actually cause political trouble in one form or another.
It is also important to analyze conventions in the context of dynamic political events and understand why conventions checks and balances of our system which are designed to ensure that power never concentrates too much for too long in the same place but it keeps shifting. Some examples of constitutional conventions are: The existence of Prime Minister and Cabinet (PM not mentioned in an Act of Parliament until 1917; Cabinet not until 1937; and in both cases only in relation to salaries, see e. g.
Ministerial and Other Salaries Act 1991). In appointing a Prime Minister, the Queen should commission that person who appears best able to command the support of a stable majority in the House of Commons (not House of Lords, since 1902). The Prime Minister presents a list of his proposed ministerial colleagues for the Queen's approval. She may make observations, suggestions and objections, but the Prime Minister is entitled to insist on his own choice. The Prime Minister decides which Ministers are to be members of the Cabinet.
In the light of these consider the role of the Queen in the appointment of the First Minister of Scotland as discussed on 10th February 1998: HC Debs col 197. All Ministers must be or become members of one or other House of Parliament. The Prime Minister may require a Minister to resign at any time and for any reason he thinks fit. The Prime Minister may decide to advise the Queen to dissolve Parliament without prior reference to Cabinet The Government must maintain the confidence of the House of Commons.
If a 'motion of confidence' on a matter central to government policy is lost, the Government must resign or PM must advise the Queen to dissolve Parliament. The Ministers are individually and collectively responsible to Parliament (nb regarding collective responsibility: unanimity, solidarity, confidentiality). A very good and detailed account is to be found in Peter Hennessy's lecture: The importance of being collective – Cabinet Government since 1945 (21st June 1995, Kingston University). In the UK, a sovereign has not refused assent to a bill since Queen Anne refused her assent to the Scottish Militia Bill in 1707.
The existing constitutional convention is that the Queen must assent to every bill passed by the Houses of Parliament. Cconventions are familiar with people and recognized by the British Constitution. Some examples of how conventions are used are:1. the prime minister can choose the day and the way of his election 2. the importance of the media and how they can influence the decisions of conventions and 3. that Conventions are considered the office of Prime Ministers and the Cabinet which are responsible for the things that their employees do and also responsible to parliament.
It is also important at this point to mention conventions in practice, which are: Kilbrandon Committee considered the constitutional status of Guernsey and convention of Parliament not legislating for it. Reference Re Amendment of the Constitution of Canada (1982) 125 DLR (3d), majority of the Supreme Court of Canada. Madzimbamuto v Lardner-Burke et al,  1 AC 645, Lord Reid. Attorney-General v Jonathan Cape Ltd  QB 752. Lord Widgery, CJ. Memorandum of Understanding between the United Kingdom and Scottish Ministers (1999) Cm 4444 and Scotland Act 1998, s.28 (7) convention of non-interference by Westminster in Scottish affairs innovated by Lord Sewll.
The Salisbury convention suggests that the House of Lords (not being an elected chamber) should defer to the House of Commons. The precise scope of this convention is debated 29th March 2000: HL Debs cols 838-840 and is illuminating about conventions in action. Section 4, Statute of Westminster 1931 limits the powers of Parliament to legislate for colonies. Section 1, Northern Ireland Constitution Act 1973 enshrines the limitation on Westminster giving up Northern Ireland without the consent of the people of Northern Ireland.
However, note, the absence of means of enforcement and also the fact the that the section has subsequently been modified. Judge Over Your Shoulder official guide for government on how to keep within the law. The Ponsonby rule is essentially a documented convention which deals with the status of international law in the UK constitution. Codification of Conventions Many conventions already in writing, for example Ministerial Code, Sewell Convention, Ponsonby Rules and Statute of Westminster 1931.
The first asserts that conventions should both be codified and given legal force, perhaps within a written constitution. Alternatively, conventions might be codified within an authoritative text with no legal status (soft codification) and so remain as non-legal political simply in order to clarify them. Codification was adopted by Australia in relation to 34 conventions, see for interest C J G Sampford, "Recognize and Declare": an Australian Experience in Codifying Constitutional Conventions.  OJLS Limitations on Government Power
The conservative government advocated a supposed distinction between ministerial responsibility and ministerial accountability which was probably intended to limit the then existing conventional obligations of ministers. Taking Forward Continuity and Change Cm 2748 pp 27-8; see also the Armstrong Memorandum of 1st December 1987. The accountability/responsibility distinction was in substance accepted by the Scott Inquiry (Report of the Inquiry into the Export of Defence Equipment and Dual-Use Goods to Iraq and Related Prosecutions HC (1995-1996) 115 Section K Vol.IV) and Sir Richard Scott writing extra judicially  PL 410.
But it has not been universally upheld: see The 2nd Report of the Public Service Committee (1995-6) HC 313, para 21 which rejected the difference between accountability and responsibility and doubted whether in practice such a distinction could be made. Ministerial accountability is governed by the Ministerial Code, Cabinet Office July 1997, and the Resolutions of the House of Commons and House of Lords on ministerial accountability (H. C. Debs. , vol.292 cols. 1046-7, March 19th 1997; HL Debs. , cols. 1055-62, March 20th 1997.
Conventions mean that certain practices of politicians vary legal rules. It is clear that the Sovereign's legal powers are vastly different in substance from those which she is constitutionally permitted to exercise. Sometimes ignoring convention effectively undermines the democratic process. Report of the Inquiry into the Export of Defence Equipment and Dual-Use Goods to Iraq and Related Prosecutions HC (1995-1996) 115, K8. 1 para. 27.
T R S Allan, Law, Liberty and Justice, (Clarendon 1992) suggests that in recognising a convention the courts may express approval for the principle that underlies it. He argues, the law/practise dichotomy disintegrates where courts evolve a legal rule which underpins a convention. Courts can convert important practices into rules of law. Examples of this include Carltona Ltd v. Commissioner for Works  2 All ER 560, Lord Green MR, R v. Home Secretary ex p Ruddock  2 All 518 and A-G v. Jonathan Cape Ltd  QB 752.
Giving a clear and minutely definition of conventions and to what extent are conventions a recognised source of the British Constitution is not easy and is also an endless subject to discuss. It should be noted that conventions are a remarkable source for the British constitution as although are not legal binding can actually constitute the English legal system. It's also clear that not following them would produce political difficulties and might possibly result in considerable instability they help fill the gap between constitutional formality and political reality.