2000 Rover 25 abs/brakes

I've had the following problem for about a year now. Most times when i brake (general braking, not excessively hard) i feel a sensation that i can only describe as 'grinding' and i can hear it loudly too. Obviously this means i have to leave huge braking distances in order to stop as i don't slow down as quickly as i should. I've tried taking my foot off and trying again but most time this doesn't help. The longer i leave my foot on the pedal, the worse the feeling and noise gets to the point where i judder to a stop. I have taken it to 3 garages where numerous mechanics have driven it and experienced the problem but cannot tell me what it is (and yes they are qualified!!). I've had new disks and pads and everything cleaned thoroughly and nobody can find anything wrong!
However, in the last few months the ABS light comes on and stays on but this seems to happen more so if i reach 90 miles an hour (of course i only do this private ground! lol).
The local garages are starting to groan in horror when i pull up in my little car so please can anyone give me any suggestions of what it might be so that i can tell them what to look for? Also, does it sound costly?!
Cheers,
Lisa