2. The appropriate sum, calculated as aforesaid, shall be increased by an amount equal to the compound interest which would have been payable thereon had the sum become payable on 1st July 1950 and such interest, calculated at 3½% per annum with yearly rests, had been payable in respect of the period beginning with that date and ending—
(a)in the case of a policeman who was in receipt of a pension on 6th November 1979, immediately before 1st April 1975 or the date of his retirement, whichever is the later;
(b)in any other case, immediately before payment of the appropriate sum: