7. Where—
(a)a period of employment of a retired teacher which was not non-participating employment or in respect of which a payment in lieu of contributions had been made is treated as reckonable service by virtue of interchange provisions, and
(b)the Secretary of State is informed of the amount by which his pension under the pension scheme applicable to him before interchange provisions applied to him would have been reduced in respect of that period by reason of graduated retirement benefit payable under the Act or of the method of calculating such reduction,
the retirement pension in respect of that period is reduced by that amount or by an amount calculated in accordance with that method, as the case may be, and no reduction is to be made under paragraph 5 or 6 in respect of that period.