Kirsty got any pics of your car - front and back? As the valance im selling (that you PM'd me about) will only fit A3's where the rear bumper is a complete kit rather than split into 2. Below is a pic of my car with the valance on. As you can see my bumper is 1 piece and just the valance pops in/out. Whereas the picture below is one of the S3 and you can clearly see the bumper is split into 2 pieces, the bumper and then a line and then the rear diffuser.
My car (at the garage!)
Audi S3 with split bumper
Audi Sport (solid bumper - my valance for sale will fit this style)
Audi Sport (split bumper)
You can clearly see the line where the bumper splits into 2 pieces.
Hey Kirsty im looking to do this with my audi a3 2010 aswel, mines is s-line though, so if you get any more info i'd be interested to see how easy it is to do this. I'll let you know if i manage to do mine