Decoding the Status Determination Statement (SDS) and Your Right to Appeal

A Status Determination Statement (SDS) is the document the end-client must issue to a limited company contractor before the engagement starts under the off-payroll working rules (Chapter 10, ITEPA 2003). It states the client's view of whether the engagement is inside or outside IR35, and the reasons. The SDS is binding on the fee-payer for tax deduction purposes only until the contractor challenges it. The right to challenge is statutory, time-limited, and routinely under-exercised.

This piece walks the structure of an SDS, the contractor's 45-day challenge window, the evidence to assemble, and the realistic outcomes when a challenge is well-evidenced. Sister pieces in [the IR35 hub](/guide/ir35-off-payroll-guide/) cover [the underlying take-home maths](/blog/inside-vs-outside-ir35-take-home/) and [the MOO and substitution tests](/blog/mutuality-of-obligation-substitution/).

What an SDS must contain

A valid SDS under the legislation must state the determination (inside or outside), the reasons supporting it, and be issued with reasonable care. "Reasonable care" is the statutory test; without it, the SDS is invalid and the end-client (not the fee-payer) carries the tax risk. Blanket determinations applied without case-by-case assessment routinely fail the reasonable care test.

• The end-client's view of status: inside or outside IR35 for this specific engagement.
• A written reason for the determination, not a generic template clause.
• Reference to the actual working practices reviewed, not just the written contract.
• A copy sent to both the contractor and the next party in the supply chain (typically the agency or fee-payer).
• A date of issue, used to start the 45-day challenge window.

The 45-day statutory disagreement window

A contractor who disagrees with the SDS issues a written representation to the end-client setting out the reasons. The end-client has 45 days from receipt of the representation to respond in writing, either confirming the original determination with reasons or issuing a revised SDS. Failing to respond within 45 days transfers tax liability up the supply chain to the end-client.

The 45-day clock is the contractor's structural leverage. End-clients with blanket "inside" determinations are exposed if they cannot defend the reasonable care standard within the window. A well-evidenced challenge often results in a revised "outside" SDS rather than the client absorbing the tax risk.

Evidence that moves an SDS

The substantive tests behind any IR35 determination are personal service, control, and Mutuality of Obligation. A representation that systematically rebuts the client's view across all three tests, with documentary support, is materially more likely to succeed than a generic legal letter.

• Substitution: written record of an agreed unconditional right of substitution, ideally with an example of substitution being offered or used.
• Control: contract clauses and emails showing the contractor decides hours, methods, location, and sequence of work.
• MOO: evidence that the client has no obligation to offer further work and the contractor has no obligation to accept it.
• Financial risk: insurance, equipment purchase, fixed-price elements, payment-on-deliverable clauses.
• Part-and-parcel evidence: contractor not on the team org chart, no internal email account beyond access, no involvement in client appraisal cycles.

When the SDS is invalid

What if the end-client refuses to revise?

There is no statutory appeal beyond the disagreement process. If the end-client refuses to revise, the contractor's practical options are: accept the inside determination and operate accordingly, decline the engagement, or escalate by [defending the outside-IR35 position through a robust contract](/blog/b2b-contracts-defend-outside-ir35/) for a future engagement. HMRC tribunal cases on contractor-side challenges to an "inside" SDS are rare; the contractor has not paid the tax, so there is no tax assessment to challenge through First-tier Tribunal.

Do I need a lawyer to issue the disagreement?

No, but a written representation prepared with input from a specialist IR35 advisor materially outperforms a contractor-drafted letter. The cost of a specialist review is typically £400 to £900, which is recovered many times over if the SDS is revised. For day rates above £600, the ROI on professional input is decisive.

What about CEST output?

The HMRC Check Employment Status for Tax (CEST) tool produces an indicative output, not a binding determination. HMRC has stated it will stand by CEST output if the inputs are accurate and the result is "outside", but courts and tribunals consistently find that CEST under-weights MOO and over-weights control. End-clients relying solely on CEST without further review have repeatedly failed the reasonable care test. See [why CEST is structurally flawed](/blog/hmrc-cest-tool-flawed-protect-status/) for the detailed analysis.

Does an inside SDS affect my Ltd company?

For the inside-IR35 contract itself, the fee-payer deducts PAYE and NI before payment reaches the Ltd, so the Ltd receives net rather than gross income. The Ltd should not double-tax this revenue on the Corporation Tax return. The receipt is treated as taxed employment income passing through, and the [accountant for the contractor](/services/limited-company-accounts/) reconciles this on the year-end accounts. Other contracts held by the Ltd are unaffected.