Per ANO 2009 Section 51, the exemption from holding an operator's licence is that the person operating the radio is "being trained in an aircraft registered in the United Kingdom to perform duties as a member of the flight crew of an aircraft and is authorised to operate the radiotelephony station by the holder of the licence granted for that station under any enactment"
Whilst this may be more honoured in the breach than the observance it does seem to rule out anything other than persons flying with a qualified instructor on a training flight.
It is also rather sad that I had nothing better to do on a Saturday night than look that up.
