The point is that they haven't made such a law; it's a very old one which really should be allowed to fall into disuse, as so many have; the main problem is that the law is, in some parts of the country, being enforced inappropriately.  From the point of view of Government, it's a small and unimportant thing, not worth devoting parliamentary time to; what we have to do is make it clear that they are mistaken in this assumption.

Of course, it isn't anything at all to do with having, or not having, a monarchy; the issue is historical rather than constitutional.  The last time we chopped a king's head off, it didn't make a great deal of difference.