HI Jadpitts,
Thank you for your reply.
The pixelation has got better over the last ten days as two things have changed. Whether this is coincidence or causal I do not know, however -
1. Next door (I live in a terrace) had 4 large leylandii trees (approx 20m high) chopped down that were about 5 meters from my property. I wonder if these could have affected signal quality?
2. Every night I switch the box off at the power socket so it reboots every time I use it.
Streaming and on demand services were not blighted with pixelation.