Sara Tanner was a British Metropolitan Police Service officer who served in the Specialist Firearms Command (SCO19). On 1 October 2018, she was placed in charge of the operation to prevent a suicide bombing aboard a London-bound passenger train by halting and boarding it at the derelict train depot at Barnet Shed, during which she engaged in a tense standoff with the off-duty policeman David Budd as Budd attempted to convince the suicide bomber Nadia Ali to peacefully surrender whilst also attempting to prevent Tanner and the SCO19 from shooting her. Tanner was on the verge of shooting Budd when another police sniper reported that she could not get a clear shot, forcing Tanner to call in the explosives officer Karen Grove to defuse the bomb, ensuring Ali's survival.