Cockney Steve, Fair point. But to me, "dropping in" suggests a casual arrival, should it be a nice day, or if one might feel like it on the day.
Power to prohibit or restrict flying
96 (1) Where the Secretary of State deems it necessary in the public interest to restrict or
prohibit flying by reason of:
(a) the intended gathering or movement of a large number of persons;
(b) the intended holding of an aircraft race or contest or of a flying display; or
(c) national defence or any other reason affecting the public interest;
the Secretary of State may make regulations prohibiting, restricting or imposing
conditions on flights by aircraft specified in paragraph (2) flying in the circumstances
specified in paragraph (2).