Official Secrets 21 Defence available to a public officer 17A. Any person who is charged with any offence under this Act shall not be convicted if he proves that he did any such thing in the performance of his official duties or with proper authority. Power to arrest 18. (1) If any person is found committing an offence under this Act or is reasonably suspected of having committed, or has attempted to commit, or is about to commit, such an offence, he may be arrested without a warrant. (2) Without limiting the generality of subsection (1), if any person in a prohibited place is found offending or suspected of offending against this Act he may be arrested with or without a warrant, by a police officer or any member of the armed forces and shall be brought forthwith before a Magistrate to be dealt with according to law. Powers of search and seizure 19. (1) Whenever it appears to any Magistrate upon information and after such inquiry as he thinks necessary that there is reasonable cause to believe that in any place there is any evidence of the commission of an offence under this Act, he may, by warrant directed to any police officer empower such officer to enter such place, by force if necessary, and there to search for, seize and detain any such evidence. (2) Whenever it appears to any police officer not below the rank of Inspector that there is reasonable cause to believe that in any place there is concealed or deposited any evidence of the commission of an offence under this Act, or of any prescribed offence, and such police officer has reasonable grounds for believing that by reason of the delay in obtaining a search warrant the object of the search is likely to be frustrated, he may exercise in and in respect of such place all the powers mentioned in subsection (1) in as full and ample a measure as if he were empowered to do so by warrant issued under such subsection.