Well bit the bullet and nipped down to euro car parts, got a couple of cheap springs and I now admit, the mot guy was right, I have lost about 2 cm of spring from the bottom of both mine

just had a look at the how to guide so will crack on and get em changed, although i'm gonna be scrapping the car in a month or so, maybe even ebay it as it has xenon lights, lsd etc.
Incidentally, when I was driving about 4 months ago, I did hear one hell of a bang in my nearside rear wheel arch but I just assumed i'd flicked a big stone up, maybe that was the bit of spring? Hope the car following didn't collect it on their window

Thankyou all for your help, if I make a mess changing the springs, i'll be back, thanks again!