You need to actually find out who the land belongs to. you can go to your local council offices and ask to see the maps of your area in the planning department. If you find out the trees are on land that the council has responsibility for (if they cut the grass there, or it's a public open space, you've gott'em bang to rights!) they must send a Tree Protection Officer to inspect the area. You will need to prove that the trees are either dangerous, or could cause a potential fault in your house (like subsidence). it's unlikely that they'll remove them just because leaves drop in your garden. I'd not recommend that you try and kill the trees. If these trees have Protection Orders on them, you'll be in big trouble if the council can prove it was you! i don't want to sound like a killjoy, but when worked for a housing association, it was damned near impossible for us to get anything done about any trees in or around our estates - but then that was Arun district council for you, and they're rubbish!