A certified copy of an approved sectional plan shall only be issued by a Surveyor-General and shall not be issued prior to the registration thereof, unless the written consent of the architect and the land surveyor concerned, or any person legally entitled to act on his behalf, is produced to the Surveyor-General: Provided that such consent shall not be required if the Surveyor-General has been supplied with evidence that such architect or land surveyor has unreasonably withheld his consent or has failed to respond in a reasonable time to a notice requesting authorisation for the issue of a certified copy.