(a)
In respect of persons who have been awarded a retirement pension under the legislation of the United Kingdom commencing before 1 July 1977 by reliance in whole or in part on the provisions of paragraph 16 of Sir Saville Garner’s letter of 8 December 1959 (which, in certain circumstances, enable persons to be treated as having paid contributions under British legislation for weeks of residence in Canada), and who on or after 1 July 1977 are in receipt of an old age security pension under the legislation of Canada, the weekly rate of that retirement pension which, but for the provisions of this paragraph, would be payable shall, with effect from 15 November 1977 or the first day of payment of the old age security pension, whichever is later, be reduced by a sum equal to the weekly rate of that old age security pension payable in respect of the first week of payment as converted into the sterling equivalent at the rate of exchange obtaining on the first day of that week. Revision of the amount of reduction shall be on the first or only date in every year, beginning on or after 1 January 1978, on which the said retirement pension under the legislation of the United Kingdom is increased in accordance with an up-rating order, and the amount of reduction shall be a sum equal to the weekly rate of the said old age security pension payable in respect of the week in which that day falls as converted into the sterling equivalent at the rate of exchange obtaining on that day. The provisions of this sub-paragraph shall not however operate so as to reduce the aggregate of pensions payable to an amount less than the amount of retirement pension which would have been payable under the legislation of the United Kingdom but for those provisions.