From CAP 168:-
A clearway need not have bearing strength and may be land or water. It may extend outside the aerodrome boundary only if the aerodrome authority establishes such control that will ensure that the clearway will be kept free from obstacles or that the clearway plane will not be infringed.
(EU OPS)
clearway’ means a defined rectangular area on the ground or water under the control of the appropriate authority, selected or prepared as a suitable area over which an aeroplane may make a portion of its initial climb to a specified height;
I'm pretty sure that at some UK airfields the clearway extends outside the airport boundary (e.g. LTN RW 26). I'm interested to know how in these cases "under control of the airport authority" is exercised? One presumes that "aerodrome boundary" is the limit of land owned by the airport.
Thanks for any help.