When a municipal council has entered into any arrangement, or made any promise, purporting to bind itself or its successors for a term of years or for an unlimited period, to continue to any educational or charitable institution a yearly contribution from the municipal property or fund, it shall be lawful for the municipal council, or its successors, with the sanction of the Government, to cancel such arrangement or promise, or to discontinue or to diminish such yearly contribution provided that it shall have given at least twelve months' notice of its intention so to do to the manager or managers of such institution.