I believe it's something to do with the 1939 Wireless Act. There were some dreadful people with funny accents on the other side of the channel who had submarines, were nasty to the French and sent spies, all called 'Fritz', to move amongst the population - taking tea at the Savoy and watching us and reporting back. 'Zey are drinking ze tea und eating all ze crumpets'. That sort of thing.
It was updated in 1949 and the current act starts, and I kid you not:
BE IT ENACTED by the Queen's most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:-
Charges for wireless telegraphy licences. 1. - (1) In this Act "wireless telegraphy licence" means any licence under the Wireless Telegraphy Act 1949 other than a television licence as defined in section 1(7) of that Act.
So any device would need me to go to Her Majesty and ask for a license to transmit the 2 feet to my radio in order to listen to 'smack my bitch up' or other popular tunes of the day.