Several people in this thread have said: presumably if you hold a radio licence (meaning a FRTOL) its legal to listen.
Actually its not, the FRTOL entitles the holder to operate a radio station in any aircraft.
The radio station itself must also have a radio station licence whether it be in an aircraft, on the ground, or even a handheld transceiver.
An operator's licence (FRTOL) is only required for aircraft operation. Ground operation is covered by the radio station licence and in certain cases the operator may be required to hold an ATCO licence or a Certificate of Competence to operate.