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 2006 (WT Act 2006). For mobile telephones, the use of the spectrum by the network operators is licensed to cover the use of transmitters and repeaters which are under their control, while user devices (i.e. handsets) are covered by a general exemption. It should be noted in particular that cellular repeaters/boosters/enhancers are not exempted devices.
Other than as used in accordance with a licence (or exemption), the use of radio equipment is illegal.
Guidance on Receive-Only Radio Scanners (PDF, 36.9 KB)