NIM09300 - Earnings Periods: Statutory Payments: Delay in paying
Section 4(1) of the Social Security Contributions and Benefits Act 1992 (SSCBA 1992)
Normally an employer pays Statutory Payments (SPs) at the time wages for the same period are, or would have been, paid. If there is some delay in paying the SP include them as part of the pay in the earnings period in which the employer pays it regardless of the period to which it relates.
This rule applies even if the employer pays the SP in a different tax year to the one in which they would have normally paid it. In these circumstances, the employer calculates the NICs using the NI rates, earnings limits and thresholds current on the date of payment even though the SP itself may be payable at one of the rates for the closed tax year.