My early 1940's house in Leeds seems to have a full complement of
plasterboard ceilings. There seems to be no evidence anywhere in the house
of fire or flood damage which I suspect might have led to the ceilings being
replaced. Also it's integrated in the appropriate places with the wooden
beading they used to use before the metal edging came about. I thought that
this period of house should have the lath and plaster ceilings.

The walls are all rendered with what I'm told is lime/sand (very dry,
crumbly stuff).

Is this plasterboard as we know it today? It has the standard white plaster
material sandwiched between two sheets of brown paper. Is it likely that
it's original - I certainly can't find any evidence to suggest otherwise.