I am swapping my black bumpers for some red colour coded ones, but some of the bolts are so rusted that the rachet just slips and it wont budge!! i cant get a tool in to cut it ! another bolt wont come out becuase the nut behind is slipping an spinning round with it, and i cnt get a spanner in to stop it! help please anyone??

cheers

heat,heat and more heat.
applied carefully as its near the petrol tank and be aware of heat transfer from the bolts to the plastic bumper.
a good soaking in penetrating oil overnight will help

or grind them off if you can access them