The expensive cars parked outside their Central London headquarters would grace any self-respecting gangster’s garage — and may well have done, since many have been seized from criminals.

For much of the time the officers are disguised and out of the public gaze, but when they are spotted it is often in dramatic circumstances: SFO officers disguised as cleaners and workmen rushed and captured the gang about to steal the £200 million Millennium Diamond from the Dome.

Each of the 80 to 100 officers in the unit is chosen for the special duties after proving himself as an ordinary marksman and then working as a member of an armed response team. They then undergo new training, including working with the SAS, and attend frequent refresher courses.

They learn abseiling, streetcraft, high-speed driving skills as well as close-combat and siege tactics. They also have rest periods as trainers to ensure that they never get stale.

They carry a cut-down version of the Heckler & Koch carbine, which can be hidden under a coat or jacket, and the Austrian-made Glock automatic, which has become a standard weapon.

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