This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

National Insurance Manual

Refunds: Class 1: NICs paid in error: Error occurred within recently ended tax year

Real Time Information Years

If an employer discovers, on or before 19 April following the end of the tax year, that he has not submitted an FPS or has reported incorrect year to date figures, he should submit an additional FPS with corrected year to date figures as at 5 April for the tax year in question.

If the employer discovers the issue on or after 20 April in the following tax year, he should submit an EYU. An EYU can be submitted to correct FPS information for up to 6 years after the original FPS or EPS was filed.

Guidance on how to do this can be found in CWG2 Employers Further Guide to PAYE and National Insurance contributions ”Fix Problems with running Payroll”.

If an EYU is submitted which amends figures downwards (a refund is due) the employer has the option of refunding the money directly to the employee or requesting that the refund is made by HMRC by writing to:

National Insurance Contributions and Employer Office 
HM Revenue and Customs 
BX9 1AN 
United Kingdom

Pre RTI Years

If the employer has made mistakes in a recently ended tax year and they have not sent in their end of year return and final payment, they may make the refund adjust their records and correct any mistakes in the current tax year.