Thanks for your reply. How did you establish contact with someone at Openreach who could discuss and agree your plan?
Applied via normal process (Cerberus) and asked for a note to be stuck on the file for the surveyor to contact us, then collared him when he was here. He was always going to knock on the door as needed to measure to house from entrance, circa 150m. He asked if I wanted them to dig the garden up and if so what route, or if I wanted to do it. He was quite relieved when I said we would do it as I didn't want their contractors making a mess. Turns out he didn't want his contractors making a mess either.
First shot is the easy bit. There is a point where it goes under fence, through a flower bed, cross a cottage lawn, then under another fence, then runs along under a path, then turns right to go through a brick walled greenhouse, and into the house.