A Status Determination Statement (SDS) is the document a medium or large end client must issue under Chapter 10 for each engagement, stating its conclusion on whether the contractor is inside or outside IR35, together with the reasons for that conclusion. The conclusion must be reached with reasonable care.
The client must pass the SDS to both the worker and the next party in the chain (the agency or fee-payer). Two consequences flow from getting this wrong. If the client does not take reasonable care, the SDS is invalid and the client itself becomes the deemed employer liable for the PAYE and NIC. If the client fails to pass the SDS down the chain, the liability sits with the client until it does.
A worker who disagrees can use the client-led disagreement process: the client must consider the representations and respond within 45 days, either confirming the SDS with reasons or issuing a new one. A client that issues a blanket determination across a whole category of roles without individual assessment is very likely failing the reasonable-care requirement. The statutory hook is ITEPA 2003 s.61NA.