law: 243. Lapse of sanction.
  Every sanction for the erection or re-erection of a building given or deemed to have been given as herein before provided shall be available for two years from the date on which it is given, and, if the building so sanctioned is not begun by the person who has obtained the sanction or someone lawfully claiming under him within that period, it shall not thereafter be begun unless the Chief Executive Officer, on application made there for has allowed an extension of that period.