As far as I know there have been investigations into the Google wifi case but I have never heard of anything coming out of it.
The law in its current form is pretty new, it even was clarified just a few months ago to specifically mention non-acoustic communication.
I'm not sure if this is the relevant legislation but I've found the following in section 48 of the Wireless Telegraphy Act 2006:
A person commits an offence if, otherwise than under the authority of a designated person—
(a) he uses wireless telegraphy apparatus with intent to obtain information as to the contents, sender or addressee of a message (whether sent by means of wireless telegraphy or not) of which neither he nor a person on whose behalf he is acting is an intended recipient, or
(b) he discloses information as to the contents, sender or addressee of such a message.
Source: http://www.legislation.gov.uk/ukpga/2006/36/section/48
It's pretty obvious why it was made illegal to eavesdrop police radio but less clear why airport communications are also illegal. So I find it odd (baring in mind I'm speaking from a position of ignorance - which is why I'm raising this question) that airport communications were added to what seems a pretty sparse list of excluded broadcasts.
Maybe it's just another example of laws not keeping up with technology? ie that law originates from a time when radio transmissions were pretty limited to private and public broadcasts whereas nowadays most of our private communications are also broadcasted via some frequency and waveform - albeit we now have automated encryption/decryption techniques to protect our correspondence. So if the law was written now it would be more like a whitelist of content you could listen into (eg radio and TV broadcasts) rather than a blacklist of specifics you could not. I'm just guessing here though.