Toadinthehole A lot of concern arises from the fact that Britain's constitution looks muddled and messy because it's "unwritten". All this actually means is there is no single document called "the constitution". This is a very good thing because it means lawyers can't get very rich arguing about what a bunch of men who died 200 years ago actually meant, or whether their views prevent a democratically elected goverment from doing things the majority want now (two problem our friends in the US suffer from).
It is messy. Its messy because in the last 15 years or so, there have been so many legislative amendments to it that its actually now even more difficult to say what the UK's constitution actually comprises, never mind where its found. You can certainly make an argument that that compromises legal certainty.
As for the bunch of men 200 years ago, the unwritten British constitution is actually based on a number of different written pieces of legislation which are accorded more importance, along with unwritten constitutional conventions such as parliamentary sovereignty and the division of powers. These definitely include Magna Carta in 1215 and the Bill of Rights 1689 through to the Act of Union 1707 between Scotland and England, to more recent statutes.
The British constitution is actually very simple. It is basically that there is one Parliament, which can pass whatever law it likes. It is made of three parts: the House of Commons (the boss), the House of Lords, and the monarch, all of which must agree to any laws made by Parliament. Also there is an independent judiciary that interprets what those laws mean, applying case law principles as they do so.
Its not that simple. Its arguably both a political and a legal convention, because it can be amended very easily, often as a result of political (and media) debate. Arguably also, there is a deficiency in terms of individual enforcement of their constitutional rights, as judicial review is restricted (and more restricted in Scots law than in English law, due to the requirement of personal interest).