Thanks for your replies guys. I got the fronts fitted first as the garage i got them fitted at didnt have the correct tool for fitting the rears, and noticed the improvement straight away even before the pads had bedded in.
I later had the 310mm rear disk setup fitted and now they have all bedded in the braking is amazing.
I did notice the front end diving quite a lot under heavy braking before upgrading the back brakes. My old pads were shot so this wont have helped much.
For anyone with the Cupra/S3/R32 front brakes or similar, considering upgrading the rears i would highly reccomend it!!!!
Also just to point out 17" wheels do fit over these brakes. The 17"
Leon mk2 Sport alloys i have on mine needed 5mm spacers but the A3 Sport 17"alloys go straight on without spacers with an offset of ET56