Aw, beat me to it NoNumpty lolThey are guards that protect your brake components from debris kicked up off the road from under the car. you should have some on the front and rear wheels just visible behind the disks. as can been seen just behind the disk in the picture in this post http://www.civinfo.com/forum/items-wanted/52220-type-s-splash-guards-front-rear.html
I noticed you said that yours are broken, I can't imagine how that could have happened in normal use, certainly not wear and tear. Can only think they have been used to lever off a seized disc or wheel or something similar. I would want to see them and come to my own conclusion.