Rear rack brackets on Roadster wont come off, any clues?

There are nuts behind the brackets. I had to use a large screwdriver, and gently pry the fender some, to get the 12mm wrench on the nuts.
 
I use a 3/8 drive 12mm socket and put it through the holes that are in the rear mudguard that give you access to these nuts.Saves prising the guard and damaging the paint.