I'd have to go with PPRuNe Dispatcher on this .... surely THE authority is the Government by way of the
Wireless Telegraphy Act 1949
Section 5 (snipped version) states :
Any person who:
(b) otherwise than under the authority of the Postmaster General or in the course of his duty as a servant of the Crown :
uses any wireless telegraphy apparatus with intent to obtain information as to the contents ........ of any message which neither the person using the apparatus nor any person on whose behalf he is acting is authorised by the Postmaster General to recieve
.... shall be guilty of an offence under this act.