I thought signal jamming in the UK was banned?

Under Section 8 of the Wireless Telegraphy Act 2006 it is unlawful to install or use wireless telegraphy apparatus except under a license or were subject to a specific exemption. s. 8 (1) says “A person commits an offence if he uses apparatus for the purpose of interfering with wireless telegraphy”. However, the Police Act 1997, Intelligence Services Act 1994 and the Prisons (Interference with Wireless Telegraphy) Act 2012 makes provision for the use by law enforcement agencies of apparatus that may cause interference.