Readers may recall that just before Christmas I had some amazing customer service from Virgin Media who replaced my faulty set-top box on Christmas Eve.
It didn't fix the fault.
So having eliminated a TV fault (by trying a different set), and a set-top box fault, we were left with but one conclusion - both scart leads we had tried were faulty.
Over Christmas we had a lot of guests and to make more room in the house opened the double doors in our lounge which divide it in two. So, as we were watching TV on Saturday evening, it was observed by Mrs Mustard to be strange, because we could now see the TV and the illuminated Christmas tree in the front window at the same time, that the digital interference on screen coincided with the flashing of the Christmas tree lights. Lights which had not been turned on at the time of the engineer's early visit.
Apologies Virgin. It is our circuits that need fixing, not your set-top boxes or signal. We grovel.