It is not enough to have a written contract that is outside of IR35. Your practical working arrangements must comply with the terms of the written contract, so that they are also outside of IR35. For instance, if your contract says that you have a right of substitution, then you must be able to put this into practice. If you are working through an agency, you should ensure that the terms of your contract with the agency are mirrored in the terms of the agreement between the agency and their client. It is recommended that you ask the end client to confirm in writing the nature of your working arrangements.
In
Usetech Ltd v Young the High Court decision made it clear that the "upper level" contract between the agency and the end client was to be considered in deciding the status of the worker, notwithstanding the terms of the agency's contract with the worker's Personal Service Company.
If you are subject to a status enquiry by HM Revenue & Customs, the Status Inspector will normally want to obtain information from both you and the end client about the practical working arrangements of each engagement. This is known as constructing the "hypothetical contract" between the worker and the client. It is vital therefore that there is a clear understanding between you and the client about the nature of your day-to-day working relationship. This will also apply to situations where there is no written contract.
Qdos Consulting can assist you in drawing up contractual terms that are IR35 compliant, and in preparing a form or statement that you can use to obtain the end client's confirmation of the practical working arrangements.