I came across an unusual fault with a Freeview digital TV over the holidays that I thought I would post the solution to in case anybody else comes across this. The set was a wall mounted Logik (Currys own brand) L22LDVB21 22 inch with built in DVD player. Occasionally the picture would pixelate and break up as if the signal was dropping out, yet it was in a very strong signal area and the signal strength was very good. I checked the antenna connections and the plug to the back of the set and the wall socket were correctly in place. When I touched the edge of the set there was a static discharge and the picture came back perfectly. After a while the picture broke up again and after touching the side it came back.
It appears that the set is lacking an earth. The power comes from a 12v power supply pugged into the wall so there is no direct mains earth. I think the TV distribution amplifier may have the "earth" side of the aerial cable sitting above earth. Either way there is an insufficient earth, probably made worse by having the set wall mounted. I am going to try earthing the earth side of the wall TV aerial socket to a radiator, assuming that's a better earth, and see what happens.