We have a 1936 house with plasterboard ceilings in all rooms
(original). It looks slightly unusual compared to modern plasterboard
- thinner board with thicker coarser paper and the plaster contains
what looks like small chips of wood. I was slightly suspicious that it
might have contained asbestos and as I was going to bring down a
ceiling I had it tested - it did not contain any asbestos. On further
investigation on the Net it became clear that plasterboard was in fact
produced in the UK from 1917.

Alan