Hi I've been with virgin nearly 12 months and we have a TiVo box in the living room. We've noticed that a selection of channels are very pixelated and some we don't have any picture at all. We had an engineer come on Tuesday this week and at the time the issue went away. However when I came home from work I found the issue was back. At the moment there are 10 channels that are pixelated and 3 more channels that have no picture what so ever. I'm really not impressed with the tv service.
I have had a similar problem in the past. Obviously I don't know if it's exactly the same fault but after several engineer visits (including a change of box), it was a fading amplifier within the street cabinet. Once replaced everything was fine again.