Isn't there a separate licence now for a handheld? I seem to recall the CAA taking over from the RA the licensing of aircraft radios, reducing the aircraft licence fee slightly, and introducing a separate licence requirement for handhelds.
I queried the need for a separate licence for mine, and was told I didn't need one if I only used the handheld inside the aircraft.
Rather implies you can use a handheld elsewhere (though what callsign you'd use is beyond me).