Legal Listening
Whether or not listening to air traffic radio is legal I would place in the same file as listening to Police radio - whereby for every Yes - there
will also be a 'No' !
Ham Radio (Amateur Radio) licence holders will often quote the 1948
Wireless Telegraphy Act and state that the practice 'Is Illegal' !
However if seeking an answer from your local police station (as I once did)
will leave you further confused as they dont seem to know for sure either.
I have heard it summed up that 'Provided one does not act upon or use
any information gained by listening in' then it is not illegal.