40. Whenever it appears to the Police Commissioner that the movement or encampment of any gang or body of persons in any place is causing or is likely to cause danger or alarm or reasonable suspicion that unlawful designs are entertained by such gang or body or by members thereof, he may, by order in writing, direct the members of such gang or body so to conduct themselves as may seem necessary in order to prevent violence and alarm, or to disperse and remove themselves outside the Metropolitan Area within such time as he may specify and not to enter or return to the said Area.