int_19h parent
It's not meaningfully a constitution if it can be overridden in practice by a simple parliamentary majority vote, same as any other law. It's more like the "constitutions" that some absolute monarchies have or had in the past where the first thing is does is declare the monarch above any limits, just not quite as overt.
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.