Cast: Peter Firth, Richard Armitage, Nicola Walker, Sophia Myles, Max Brown, Shazad Latif, Rupert Penry-Jones, Hugh Simon, Hermione Norris, Miranda Raison, Keely Hawes, Matthew Macfadyen, David Oyelowo, Robert Glenister, Anna Chancellor, Alex Lanipekun, Gemma Jones, Raza Jaffrey, Olga Sosnovska, Rory MacGregor
- Airs: 9pm Mondays
- Air Dates: May 2002 - October 2011
Follows the actions of MI5's counter-terrorism department in London. Led by the uncompromising Harry Pearce, the team race to stop dangerous attacks from rogue terrorists and conflicting intelligence operations of other countries like the US, Russia and various Middle Eastern regimes. Those with plans that threaten the stability of United Kingdom will face this tough group and their various operatives who will sacrifice their lives in the name of their duty. A trademark of the series is its frequent refreshing of the ensemble cast, which means any character can die at anytime. Within the first seven seasons nearly a dozen regular or recurring cast members have been killed off or 'disappeared off the grid', including several former leading stars.