Threat Levels / MI5, 30 June 2007
http://www.mi5.gov.uk/output/Page311.html
"Current threat level: CRITICAL
This means that an attack is expected imminently and indicates an extremely high level of threat to the UK.
See The UK's threat level system for more information on what threat levels mean, who decides the level of threat and how the threat level system is used."
How can you help / MI5, 2007
https://www.mi5.gov.uk/output/Page18.html