the compensation shall consist of an annual sum which shall be payable at intervals equivalent to those at which the emoluments of the claimant's employment are or were previously paid, and shall, subject to Regulation 20, continue to be payable until normal pensionable age; and

the said annual sum shall not exceed the figure which bears to the maximum annual sum which could have been awarded under Regulation 13, had the claim been for compensation for loss of emoluments, the same ratio as the amount of the diminution (calculated as an annual rate) bears to the amount of his current net emoluments, but so however that no compensation shall be payable if this ratio is less than two and half per cent.