CSLM13018 - FAQs: forms questions and answers: retention of records of SL deductions
Suggested answer
You should keep a record of what you pay your employees and the deductions you make.
You need to keep them for 3 years from the end of the tax year they relate to. HMRC may check records to make sure the right amount of dedcutions have been taken
Information on keeping records can be found https://www.gov.uk/paye-for-employers/keeping-records