21.—(1) A licence, notice, approval or authorisation under this Order or the Scheme, as the case may be, shall be in writing, may be general or specific, may be subject to conditions and may be amended, suspended or revoked by notice at any time, and in particular may be suspended or revoked if the Department is of the reasonable opinion that the provisions of this Order or the Scheme are not being complied with.
(2) A person on whom a notice is served or to whom an approval or authorisation is granted under this Order or the Scheme shall comply with its requirements.