It can be fairly confusing knowing if you’re allowed to listen to ATC/Aircraft communications. Equipment and information is freely available, and there are websites which stream ATC communications – here is some clarification about the UK law.
Is it legal to own a scanner? Yes – a license is required when owning a transmitter, but radio recievers require no license.
Is it legal to listen to ATC in the UK? It depend upon the specific circumstances.
What transmissions can I listen to? Any transmission intended for you or for general reception. This would mean, ATIS announcements, and by some interpretation, emergency broadcasts.
So it is illegal to listen in on ATC communications between ATC and pilots if you’re not required to be listening (for instance, if you’re flying in the same region).
You can listen to ATC if given permission, e.g. at an air show.