Hi NT
I can see where you are coming from.
To suggest an open plan room and its different constituent areas (ie lounge, kitchen) consitute inner / access room without any physical boundary seems bizare.
The definition of a "room" (according to Building Regs E&W) is "An enclosed space within a building that is not used solely as a "circulation space".
Definition of "circulation space" (BRegs Again) is "A space (including a protected stairway) mainly used as a means of acess between a room and an exit from building and compartment.
To me it seems BC are trying to suggest the "hall" part of the open space is the access room, which is ludicrous. Is that your interpretation NT?
Back to your original question I think Piglet is right. I doubt there will be any other definition in legalese. In my experience courts will look at definitions from published guidance, and whilst they expand on such definitions, I know of no example of this relating to inner room scenarios, as the definition is, I think, quite black and white.