My boring 2p worth, vintage ATCO's link to the Radio Agnecy's site says:
Anyone who intends to listen to radio transmissions should be aware of the following:
A licence is not required for a radio receiver as long as it is not capable of transmission as well (The Wireless Telegraphy Apparatus (Receivers) (Exemption) Regulations 1989 (SI 1989 No 123). The exception to this is that it is an offence to listen to unlicensed broadcasters (pirates) without a licence. Licences are not issued for this purpose.
Although it is not illegal to sell, buy or own a scanning or other receiver in the UK, it must only be used to listen to transmissions meant for GENERAL RECEPTION. The services that you can listen to include Amateur and Citizens' Band transmissions, licensed broadcast radio and weather and navigation broadcasts.
It is an offence to listen to any other radio services unless you are authorised by a designated person to do so.
So, what is a navigation broadcast?
At the end of the day, like everyone else says, noone will (or rather is unlikely to) lock you up for listening to your local tower. I sometimes tune in to Heathrow approach and listen to a one-sided conversation as the pilots report in, or reply. Gets tedious.