11(1)Where an authorisation has been given under section 326(8) the Treasury may vary the conditions and stipulate the date on which the variation is to become effective; and the variation shall have effect as regards any contract entered into on or after the stipulated date.
(2)No variation under this paragraph shall be effective unless the Treasury—
(a)send a notice by post to the society or institution concerned informing it of the variation, and
(b)do so not less than 28 days before the stipulated date.