Thanks for the replies.
Mixture maybe that is the way to go. Cable it. I could cable through the roof space with an ugly conduit down the wall, or go the whole way and chisel it under the plaster. Or perhaps a cable to above the room and then a wifi Tx at that point to transmit down? It is only plasterboard ceiling that I need to penetrate.
We get dreadful mbps rates here (South Africa at the end of a valley) so I'm only trying to put lipstick on a pig.