Well, as we all know the bigger your brake discs are, the quicker you can bring a car to a halt. As standard the Clio 16v and Williams discs are 259mm on the front, and 238mm on the rear. They fit nicely under the 15" rims, and are a pretty good combination that's perfectly capable for the car.
However, bigger can always be better.
A couple of Renault tuners offer a 285mm big disc conversion. With a bit of research I found out that the discs they use are from a Renault 21. With a different set of caliper mounts and a bracket it looks like the discs will fit.
So, a chap on RSC set about making up some brackets. They're being made from HE30 billet alloy so they'll be nice and light. I've already got the discs, so it's just a case of waiting for the bracket and then putting it all together!