If the whole or any part of any budget grant included in the budget estimate for a year remains unexpended at the close of that year, and the amount thereof has not been taken into account in the opening balance entered in the budget estimate of any of the next two following years, the Commissioner may sanction the expenditure of such budget grant or the unexpended portion thereof during the next two following years for the completion of the purpose or object for which the budget grant was originally made and not for any other purpose or object.