Nigel's comments are probably true - so many times when I check these BT design items at Kew, it is almost always the shape that is the subject of the Registration. In the attached pic showing specific wording for a Stuart design (by coincidence), you can see how the final sentence - which is standard on virtually all Registrations - indicates that the 'novelty is in the shape etc.'.
I can include this one when next I visit the Archives if it's of interest.
John's 'small jug' is a Stuart piece that I've also had in the past - long since given away I'm sure, and I forget the size now - mine did have a small inset lid, as shown in the attached pic. and it had the Woodchester cut design. I forget now whether is was marked with an Rd. No. or not
The shape of these small Stuart jugs is distinctive.