HMRC has two reference checkers for PAYE and Class 1 and Class 1A NICs:
PAYE and Class 1 NIC - current year monthly or quarterly payments
For use when you are making your current year monthly or quarterly PAYE and Class 1 NICs payments.
PAYE, Class 1 and Class 1A NIC - previous year payments
For use when you are making a PAYE and Class 1 NICs payment, or a Class 1A NICs payment, for a previous year.