Any notice or other document authorised or required to be served under this Act may, without prejudice to any other method of service, be served by registered or recorded delivery post; and for the purpose of the application to this section of section 26 of the [1889 c. 63.] Interpretation Act 1889 (which relates to service by post) the proper address of a person to whose registration such a notice or other document relates shall, if he is a registered person, be his address on the register.