The UK licensing authority
The UK government department responsible for issuing radio licences and
enforcing legal proceedings against people carrying out unauthorised transmitting or
receiving is called Ofcom (Office of Communications). Previously, it had
been the Postmaster General (PMG), the Home Office (HO), the Ministry of Posts
and Telecommunications (MPT), the Department of
Trade and Industry (DTI) and the Radiocommunications Agency (RA).
Ofcom issue many types of radio licence, including licences for businesses,
the emergency services and Radio Amateurs.
You need a licence
In the UK the use of any radio transmitting device is required to be either
licensed or specifically exempted from licensing under the Wireless Telegraphy
Act 1949. For cellular telephones, the use of the spectrum by the network
operators is licensed to cover the use of base stations, while user devices
(i.e. mobile phones) are covered by a general exemption.
You can't listen to any radio transmission you like and
you can't transmit on any radio frequency you like. You even need a
licence to own (i.e. have in your possession) as well as to use such equipment.
The Ofcom
man won't care if you say that your computerised scanner radio with lots of
coloured flashing lights and dials which is tuned to a police channel or a taxi
channel is never turned on. You have committed an offence by selecting a
channel you are not authorised to receive. He also won't care if your TV in the corner of the room "is never
used". You have committed an offence by having it in your
keeping or possession if you don't
have a TV licence. There are laws about having radio equipment in your
possession and other laws about using it.
You don't need a licence
An exception is the PMR446 specification. These are type approved low
power hand portable transceivers and can be owned and used licence-free. Another exception is
listening to radio transmissions from licensed Radio Amateurs. Another
exception is listening to radio transmissions from licensed entertainment
broadcasting stations.

Ofcom
The
use of scanning receivers Radio
transmitters