Listen as much as you like. In the UK, Australia, Canada, the US, basically it's a free-for-all.
The authorities are far too busy with other more consequential matters than trying to "foxhunt" people using scanners to listen illegally to transmissions.
During WW2 the German signal corps had a saying about radio traffic of any sort (apologies for very poor German) "Alle funkverkehr ist landsveraat" which broadly translates as "all radio traffic is high treason".
A court in the US ruled that once a radio signal propogates through the air or in free space it is in the public domain and if a person has the necessary technical skill and facilities to receive it, either by direct intent or fortuitously, then the originator of that radio transmission has no recourse.
I listen all the time. I also downlink satellite transmissions, frequently in full view of the local Police and, on occasions, radio regulatory personnel. They couldn't care less.