Every Police Officer shall, for all purposes in this Act contained, be considered to be always on duty and shall have the powers of a Police Officer in every part of the General Police District. It shall be his duty to use his best endeavours and ability to prevent all crimes, offences, and public nuisances; to preserve the peace; to apprehend disorderly and suspicious character; to detect and bring offenders to justice; to collect and communicate intelligence affecting the public peace; and promptly to obey and execute all orders and warrants lawfully issued to him.