[0]Edit: There seem to be objections to my use of the term "unconstitutional." They have ruled it as against common law:
“The aversion to general warrants is one of the basic principles on which the law of the United Kingdom is founded. As such, it may not be overridden by statute unless the wording of the statute makes clear that Parliament intended to do so.”
These sort of "basic principles" are often referred to as the British constitution or constitutional principles, so I believe my choice of term is correct even if there is no single written document called the "constitution." As to the question of whether parliament can overrule it, perhaps, technically, yes, but I find it very difficult to come up with a scenario that would successfully meet the objections in the ruling.