any notice or other document is required to be given or sent to the clerk to an appeal tribunal, the Secretary of State or the relevant authority, that notice or document shall be treated as having been so given or sent on the day that it is received by the clerk to the appeal tribunal, the Secretary of State or the relevant authority, as the case may be; and

any notice (including notification of a decision of a relevant authority) or other document is required to be given or sent to any person other than the clerk to an appeal tribunal, the Secretary of State or the relevant authority, as the case may be, that notice or document shall, if sent by post to that person’s last known address, be treated as having been so given or sent on the day it was posted.