21(1) A person does not commit an offence under any of sections 15 to 18 if he is acting with the express consent of a constable.
21(2) Subject to subsections (3) and (4), a person does not commit an offence under any of sections 15 to 18 by involvement in a transaction or arrangement relating to money or other property if he discloses to a constable–
(a)his suspicion or belief that the money or other property is terrorist property, and
(b)the information on which his suspicion or belief is based.
21(3) Subsection (2) applies only where a person makes a disclosure–
(a)after he becomes concerned in the transaction concerned,