Clause 19

Every person subject to military law who obstructs or, when called upon, refuses to assist any military policeman or person legally exercising authority under or on behalf of a military policeman shall be guilty of an offence and shall be liable on conviction by a subordinate military court to imprisonment for a term not exceeding two years or any less punishment authorised by this Act except that it shall be a defence for any person charged under this section to prove that he neither knew nor had reasonable cause to believe that the person in relation to whom the offence is alleged to have been committed was a military policeman or, as the case may be, a person legally exercising authority under, or on behalf of, a military policeman.