For the purposes of section 97(4), the value of the benefit conferred on a person (P) by a capital payment made by way of loan to P is, for each tax year in which the loan is outstanding, the amount (if any) by which—
the amount of interest that would have been payable in that year on the loan if interest had been payable on the loan at the official rate, exceeds
the amount of interest (if any) actually paid by P in that year on the loan.
In this section and section 97B the "official rate", in relation to interest, means the rate applicable from time to time under section 178 of the Finance Act 1989 for the purposes of Chapter 7 of Part 3 of ITEPA 2003.