77. Broadcasting from ships and aircraft

(1)It is unlawful—
(a)in the case of any ship or aircraft, to make a broadcast from it while it is in or over the United Kingdom or external waters; or
(b)in the case of a British-registered ship or British-registered aircraft, to make a broadcast from it while it is not in or over the United Kingdom or external waters.

Wireless Telegraphy Act 2006

Context is everything.

(yes, I know I'm being facetious and "broadcasting" is specifically defined as not to cover messages for navigation or safety)