Section 1228 | Credits that reverse debits
From legislation.gov.uk
For the purposes of sections 1229 and 1230, a credit reverses the whole or part of a debit in any case where the credit falls to be made because—
(a)the sum represented in whole or in part by the debit is paid and then wholly or partly repaid, or
(b)the sum represented by the debit is never paid.