On the second British level, Depot Saboteurs, in the area where you blow up all the fuel drums is a large brown church-looking building. Go up to the right-hand side door and throw two sticking grenades at it. Then, go up to it and press Action. Move back and throw one more grenade at the door to blow it up. Follow the stairs down to a room with a Bren, field pack, and some grenades.