The constitution is the legal framework by which a country is governed. It is not necessarily a set of super-laws that are harder to change than regular laws (although it may contain such laws). The UK is also not the only democracy where the legislature can amend parts of the constitution with a simple majority. Besides, the UK itself has a super-law that cannot be amended, which is that the parliament is sovereign and cannot be bound by a previous parliament.

Neither the monarch, nor individual Members of Parliament, are above all limits under UK law.