My hedge contains nesting bird -who issues legal order of protection on works?

A neighbour wants me to cut down a large evergreen hedge between our gardens that has an active blackbird nest in that is protected by law from any disturbance during nesting period.I have informed them i wont, that their extension foundations will have to be suitable to withstand the hedges roots on the boundary line and I wont be cutting anything on my side down.How else can I protect the hedge - the rspb or police do anything to pre-empt the workmen from touching the hedge?