Sky Digital - Extreme Pixellation

I have an Amstrad digibox which is about 3.5 years old. I receive every channel without a problem and the sound is perfect. I have good quality scarts.

The problem is that every channel has pixellation especially on bright white. It is really quite bad and does hamper viewing especially for my girlfriend as I keep shouting out 'just look at that pixellation, it's getting worse you know!!!!'

If anyone has any suggestions that would be great.

Thanks for your help

CDS