Is your area undergoing the digital switchover right now? We are in the Midlands, and have had to re-tune the Freeview box, where BBC channels have now moved to the 800 numbers. At the same time, the picture does pixellate more, and occasionally lose signal. It's part of the switchover, and when finished (19th Sept for us) they will increase the signals strength and give us Freeview HD.
Worth checking if the same thing is happening to you, and if it is retune the TV and then wait until later in the month and do it again.
Prior to that my TV was absolutely fine, and I am hoping it will be again when our switchover is complete. HTH
