Four factors are usually used to decide whether you are caught by the IR35 rule (working like an employee vs self-employed person). You are not caught by IR35 if: CONTROL: You decide how you work and it is not controlled by the client. SUBSTITUTION: If you have a genuine right to send someone else in to carry out your work. FINANCIAL RISK: If, for instance, if you make an error then you must correct it for free / your contract overruns but your original quote for the work must stand. MUTUALITY OF OBLIGATION: If you can turn work down and your agency/end client is not obliged to provide work.