Banned because if it's a squirrel, then it's a grey squirrel; an American invader which has achieved dominance over the proud British red squirrel of patriotic yumminess, so actually, the squirrel needs not a patch at all, but a severe spray painting.
Banned because spray painting would not solve the problem. The grey (sprayed red) squirrels would still spread a disease they're immune to and continue to kill 'proper' red squirrels, they would still have grey offspring and dependant on the red used, would look disturbingly out of place and horrible.