Spet0789 wrote: The key point is that they can be amended by any subsequent Parliament without any special procedure (beyond, one hopes, an elevated level of scrutiny).
This is what you said after your first edit, but before your second.
The Act can be amended, but the Declaration cannot. I have not looked at the arguments about the process for amending the Act (when it was first amended which I think was in the late 1800s), but the Act of Rights is clearly different because of the link to the Declaration.
I have seen documents relating to a court decision as to what are and what are not constitional laws, but it is true to say that constitutional laws have no real constitutional protection although were there to be an amendment to the Act of Rights which conflicted with the declaration it would raise an interesting legal question.