Unfortunately, you aren't allowed to drop anything, even a piece of paper, from an aircraft without permission. See para 2.
Dropping of articles and animals
66 (1) Articles and animals (whether or not attached to a parachute) shall not be dropped, or
permitted to drop, from an aircraft in flight so as to endanger persons or property.
(2) Subject to paragraph (3), except under and in accordance with the terms of an aerial application certificate granted under article 68 of this Order, articles and animals (whether or not attached to a parachute) shall not be dropped, or permitted to drop, to the surface from an aircraft flying over the United Kingdom.