1. Essentially, you can but back both the branches of the hedge and the roots of the hedge to the boundary line. As you own up to the boundary line, you can do what you want with this part of your land. This includes cutting back the hedge and its roots to the boundary line. Additionally, you can build a wall on your own side of the boundary line such that your wall abuts the hedge so long as you don't cross the boundary line into your neighbour's property with your wall. A trench can be dug for the wall's foundations which includes cutting out the roots of the hedge. So that you can build the wall on your side of the boundary line.
Thank very much you have confirmed what I had thought myself.
No need to resend it I have recovered it.