Ah, I've just changed my vacuum pump and guess what, that's not what's wrong with it. The downer is, that I've already changed the master cylinder and the servo unit, ( and bled it, had other people bled it, and taken it to garages to have it bled). I can only assume that it's the servo that's causing the problem, even though it's only around 6 months old. Next step is to try and change the carpets, maybe that will help!
cheers
K