For the purposes of section 36(4) of the 1965 Act (provision, where a person does not retire from regular employment on attaining pensionable age, for calculating the graduated retirement benefit payable to him from the date of his retirement) all the graduated contributions paid by a person in the income tax year in which he attained pensionable age shall be treated as having been paid before the day on which he attained that age:
Provided that where, in any case, the aggregate amount of the graduated contributions paid by him in that year exceeded the aggregate amount of graduated contributions which would have been payable by him in that part of the year which ended with the income tax week in which he attained pensionable age if, in each income tax week beginning in that part of the year, a graduated contribution as for an employment which was not a non-participating employment had been payable by him in respect of a weekly payment of remuneration made in that week at a level equal to the upper limit on the amount of weekly pay then taken into account under section 4(1)(c) of the 1965 Act as amended , the excess shall be treated as having been paid after the day on which he attained that age.