Thanks AmericanAudiophile, but we've no local TV repair guys. Despite being registered blind, I can remove the relevant part (small PCB with 3 touch switches and headphone jack), but on contacting what appears to be the main replacxement parts supplier (who operates under several different names e.g. "PartsMaster") they are less than helpful. Their site(s) have a "PCB Switch Board" but with no photo, and on contacting them by phone for a description, they just say "No idea, you'll have to contact the manufacturer". When I ask who the manufacturer is, all I get is "don't know, we'll get them to text you" (???).
So much for repairs - for he want of a simple part, the whole TV is unusable. I suppose that's progress!