London-based Olive Security provides former British Special Air Service troops--one unarmed guard for every four or so engineers who go out on a job--to drive and offer a show of muscle.

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The diaries of former deputy MI5 chief Guy Liddell provide a unique insight into the Security Service during some of the darkest days for British intelligence.

BBC: Cambridge Spies: MI5 diaries revealed

Last month, British officials announced they had enough evidence to charge Lugovoi -- a former security service agent-turned businessman -- with Litvinenko's murder.

CNN: UK slams Russia on poison killing

British police say they have amassed detailed evidence against Mr. Lugovoi, a career security service officer, and tracked a trail of polonium across Europe to his London hotel room and the upscale Mayfair bar where he met with Mr. Litvenenko when he consumed some polonium-laced tea.

WSJ: Russia Declares Litvinenko Murder Suspect a Victim