You may find that tree cutting has its own department in the REC that
does cover that area, and they will trim the tree for free around the
path of the line to ensure the security of the supply - which in turn
would allow the tree to be chopped in relative safety.
Thank you all for your replies, I will try some other tree surgeons

Just in case I wasn`t as clear as I meant to be, the REC may have their
own tree cutting department / contractors who will do anything in the
vicinity of the line for you.