Government Communications Headquarters (GCHQ)
Intelligence gathering agency.
http://www.gchq.gov.uk/

National Criminal Intelligence Service
Aims to combat the top echelons of crime and seeks.
http://www.ncis.co.uk/

Research Study Group
Secret bunkers, early warning systems, plans and propaganda.
http://www.subbrit.org.uk/rsg/index.shtml

United Kingdom Intelligence Agencies
Structure and operations.
http://www.fas.org/irp/world/uk/