 At approximately 11 : 30 on Wednesday 30 April the six heavily armed members of DRFLA stormed the Iranian Embassy building on Princes Gate , South Kensington . The gunmen quickly overpowered Police Constable Trevor Lock of the Metropolitan Police 's Diplomatic Protection Group ( DPG ) . Lock was carrying a concealed Smith & Wesson .38 @-@ calibre revolver , but was unable to draw it before he was overpowered , although he did manage to press the " panic button " on his radio . Lock was later frisked , but the gunman conducting the search did not find the constable 's weapon . He remained in possession of the revolver , and refused to remove his coat — which he told the gunmen was to " preserve his image " as a police officer — in order to keep it concealed . The officer also refused offers of food throughout the siege for fear that the weapon would be seen if he had to use the toilet and a gunman decided to escort him . 
