I have recently experienced the break-up of picture (Pixelation) and sound on certain channels. The main ones, BBC1,2, ITV, 4 and 5 are fine but others like Horror, Sfy, 4 movies and some others are doing it and its getting worse. I have followed all the self help instructions in the V booklet, from the Virgin site and the help menu on the remote.
I have replaced the scart lead and the co-axial cable from the wall socket to the splitter.
My TV is a 32” Polaroid HD Ready LED and the Virgin V HD box.
From the information you have provided I would like to arrange for someone to take a look at this for you so if you click on the purple envelope at the top right of the screen you will see a message waiting for you with further information.