EM1611 - Opening the Enquiry: Miscellaneous: Status
HMRC has a duty to ensure that people pay the correct category of tax and NIC, depending on their status.
When you undertake an SA intervention if a doubt arises as to the status of the taxpayer, you should refer to the Employment Status Manual ESM0002+ in order to determine whether they are self-employed or an employee.
You should discuss any concerns with the Status Inspector for your Business Unit.