So presumably you would have to tarmac the patch of grass as well. That is a big problem. You can more or less do what you want with your front garden as long as you comply with any covenents in your deeds. eg you might not be able to park a caravan or boat in you front garden. Your problem is getting the council to let you tarmac the grass and getting BT to relevel the box. They will not move it. (Just thought, is it a flush ground cover or one of the 4 foot high ones that are normally against walls?) If it is a footway box, they will proberbly change the cover and re level it, but at a price. I would contact the Local Planning Office (should be under your local council in the phone book), but I would be prepared to have a long wait, be out of pocket, or have to make do as best you can. Sorry I can't be more helpful.