It does mean something though; the point is that the Executive (in place of the Sovereign) can't just instruct the police to detain you on a whim - it has to be

It does mean something though; the point is that the Executive (in place of the Sovereign) can't just instruct the police to detain you on a whim - it has to be done in accordance with powers specifically granted by the people's representatives in Parliament. If you don't like the laws passed by Parliament, vote in different representatives!