If anything at the moment there really isn't such "requirements" since the VRCT is voluntary and any mentions of memberships of professional societies are desirable not mandatory. If anything other industries have requirements just think of Part P for the building trade so I doubt there would be any legal issues.
If anything for a lot of people the choice of professional body will often come down to who has the best publication and member benefits which unfortunately for IPEM the IET wins hands down with it's services including the online library. (and of course your
free cup of tea or coffee if your passing Savoy Place
)
