There`s a lot worse things going on in phoneboxes that BT should concern themselves with. If you hate phonebox caches why would you bother finding them??
"security, regulatory and environmental issues". Why not go one step further than just agreeing with BT and get the enviromental agencies involved and ban plastic boxes being placed in places of beauty. You just cant dump your old fridge off on Dartmoor even with landowner permission. By agreeing with BT`s definetion of environmental issues a plastic tupperware box is technically the same.
As for security, is having random strangers poking about in hedges and coming out with ammo cans not highly suspicious to the muggle public?
BT are quite in their right to ban caches, that is their choice. But agreeing to the reasoning i find hard to understand when it could be applied to all caches.