As there is no single document which every piece of constitutional legislation must refer to (like U.S constitution) Parliament are granted the power to enact or change any previous law. It is this specific capability that makes the British constitution flexible.
There are advantages and disadvantages to this flexibility. One advantage is that people don't get obsessed with what has previously been written and concentrates on innovation and future ideas. One disadvantage is that some constitutional acts may not be scrutinised carefully enough, which could lead to a particular government gaining too much power and achieving the ability to be tyrannical.
Another insurance of flexibility, other than the above, is that there is no higher power than Parliament. Anything which is passed through Parliament, is law. And if it refers to constitutional topics, the legislation is effectively an amendment to Britains uncodified constitution and there is not other power that can stop this. Parliament is supreme.
Unlike the U.S constitution, where the President and Congress are subordinate to the Supreme Court on any issue which involves constitutional reformation. The Supreme Courts dominant business is to insure that all legislation is 'constitutional'.
Britains lack of a Supreme Court style establishment can be seen as a constitutional advantage or disadvantage. The disadvantage is that there is no permanent constitutional checking body, which guarantees that the current Parliament do not try and manipulate what is 'British' and right to something undesirable. The Supreme Court in the USA also stops short term amendments to the constitution being made is it takes a long time and requires enormous popularity for any constitutional modification. The advantages of Britain not having a supreme court is that constitutional matters are not gravely deliberated on and carefully checked for undesirable mutation of British historical trend. Constitutional legislation is taken at face value and previous laws and acts can be ignored if they are damaging or no longer relevant to modern society. As the British constitutional is not compiled in single document it has no heritage, which one usually feels inclined to preserve for no particularly good reason.
Britain is part of the European Community, which means that it must abide by the community's laws. The European laws, if conflicting with a British law takes precedence. This is true even in cases which interfere with constitutional enactment's. Britain, when joining the European Union, gave up part of it’s sovereignty (i.e. some of it's rights to create independent constitutional revisions).
Britain is governed unitarily. This means there are no local governments within Britain which have their own sovereignty. Britain is governed by one central parliament and no other establishments (except the European Community) have superior sovereignty over it on any issue. This is different to the USA's method of government which hands over partial sovereignty to its' various states on various political decisions. I personally see the British take on this constitutional issue as advantageous as it rules out any possibility of their being inequality and sectional tension within a nation.
Finally Britains parliament governs under a Constitutional Monarchy. This means that all acts of parliament must be given royal assent before becoming law. This dignifies all laws and gives the British Constitution a feeling of integrity and probity despite its uncodified nature.
