For more information, refer to regulation 84H in The Income Tax (Pay As You Earn) (Amendment No. 2) Regulations 2015.
Keep any information, records and documents that demonstrate what you sent on your reports was correct, including anything that proves why you didn’t need to operate PAYE on the contractors’ payments.
Store them for at least four years and be ready to provide them to HMRC. Should they ask, you must provide evidence that proves you didn’t have to operate PAYE.