IR35 SDS: Contents, Reasonable Care, and Disputes

Under the UK’s off-payroll working rules, an IR35 Status Determination Statement is the written document a hiring organisation must give to a contractor engaged through an intermediary, stating whether the engagement falls inside or outside IR35 and explaining why. Get it right and the tax responsibilities sit where the rules intend. Get it wrong, issue it late, or fail to explain your reasoning, and you become the deemed employer, personally liable for income tax, National Insurance, and Apprenticeship Levy on every payment made to the worker.

Who Has to Issue One

The duty to produce an SDS sits with the client, not the contractor. It applies to all public authorities and to private- and voluntary-sector clients that qualify as medium or large under Chapter 10 of the Income Tax (Earnings and Pensions) Act 2003.¹ Public authorities include government departments, local authorities, NHS bodies, universities, and devolved legislatures.²

A private- or voluntary-sector organisation is small, and therefore outside the rules, if it meets two or more of these three tests: annual turnover no more than £10.2 million, balance sheet total no more than £5.1 million, and no more than 50 average employees. The turnover and balance sheet ceilings rise to £15 million and £7.5 million for financial years beginning on or after 6 April 2025, first affecting IR35 determinations in the 2026–27 tax year because size is measured against the most recently completed financial year. The employee headcount stays at 50.² Where the client is small, the contractor’s intermediary keeps responsibility for assessing IR35, as it did before the 2021 reforms. Contractors can ask a client for written confirmation of its size, and the client must respond.

Wholly overseas clients with no UK residence and no UK permanent establishment are also outside the rules, and the contractor’s intermediary again handles the assessment.²

What a Valid SDS Must Contain

Two things, both mandatory. The statement must give a conclusion: the off-payroll rules apply (inside IR35) or they do not (outside IR35). And it must give the reasons for that conclusion, drawing on employment status indicators such as the client’s control over the work, the worker’s right to send a substitute, and the actual character of the working relationship.³

A conclusion with no reasoning is not a valid SDS. HMRC treats an invalid SDS as no SDS at all, which leaves the client as the deemed employer, responsible for deducting and paying income tax, National Insurance, and any Apprenticeship Levy due until a valid statement is produced.³

Working practices carry more weight than contract wording in an HMRC investigation. If the contract says the worker sets their own hours but they actually attend the client’s office 9 to 5 every day, the reasoning in the SDS needs to grapple with that reality rather than parrot the contract.

Reaching the Determination With Reasonable Care

The client must take reasonable care in reaching the conclusion and keep records that show how the decision was made. Fail this standard and the tax liability lands on the client regardless of what the SDS says.⁴

HMRC’s free Check Employment Status for Tax tool (CEST) asks a series of questions about control, substitution rights, and financial risk, and produces a determination. HMRC has committed to standing by CEST outcomes where the information entered is accurate and consistent with its guidance, which makes the tool a practical shield if you use it honestly.⁵ It sometimes returns an “unable to determine” result and does not replace professional advice on complex or borderline engagements.

HMRC’s Employment Status Manual sets out what reasonable care looks like in practice:

Completing CEST with truthful information and applying the result.
Having someone involved who understands what the contractor actually does day-to-day.
Seeking qualified tax advice, particularly in borderline cases.
Reviewing determinations when contract terms or working practices change materially.
Confirming the accuracy of any determination work you have outsourced; responsibility stays with the client.

And what fails the standard:⁴

Blanket determinations that put every off-payroll worker inside IR35 without looking at individual circumstances.
Applying the same status to a group of workers whose arrangements actually differ.
Feeding inaccurate information into CEST.
Asking untrained staff to complete an SDS without support.
Ignoring material changes to the engagement.

Blanket determinations are where organisations most often come unstuck. HMRC may treat them as deliberate behaviour when calculating penalties, which pushes the penalty rate significantly higher.⁶

Delivering the SDS

Once finalised, the SDS goes to two parties: the worker, and the next party in the supply chain, which is usually a recruitment agency or, if there is no agency, the worker’s intermediary. Paper or electronic delivery is fine, but the worker must actually receive it or be able to access it.³

Timing matters more than most clients realise. The SDS must reach the next party in the supply chain before any payment is made for the worker’s services. Until you pass it down, you are the deemed employer, and you owe PAYE on every payment.³ That liability covers the whole period from the first payment until the day you actually deliver a valid statement; it does not disappear once you catch up. Keep an audit trail of delivery, whether that is email read receipts, signed acknowledgements, or logged access to a portal.

Handling a Disagreement

The worker and the deemed employer, typically the agency acting as fee-payer, can challenge your conclusion through the client-led disagreement process. Other parties in the supply chain cannot.⁷ A disagreement can be raised verbally or in writing.

From that point you have 45 calendar days to respond. You review the original determination in light of any new information and then either confirm the original status with further reasoning or issue a new SDS with a different conclusion.⁷

Miss the 45-day deadline and you automatically become the deemed employer for PAYE purposes, owing all tax, National Insurance, and Apprenticeship Levy due until you eventually respond. That applies even if the worker would ultimately have been found outside IR35.⁷ A calendar reminder is worth a lot of money.

What Non-Compliance Costs

The core consequence is deemed employer status. You owe the income tax and employee National Insurance that should have been deducted, employer National Insurance on top, and Apprenticeship Levy if it applies. Interest runs from the date the tax should originally have been paid.⁴

Penalties come on top and depend on the nature of the failure. Careless errors attract up to 30% of the unpaid tax. Knowingly failing to act on a correct determination can reach 70%. Active concealment can reach 100%. These figures are calculated on the full gross liability, not the net shortfall. Demonstrating reasonable care is the primary defence and can eliminate penalties entirely.

Since 6 April 2024, HMRC can offset income tax and National Insurance already paid by the worker and their intermediary against the deemed employer’s liability, so the client pays the genuine shortfall rather than the same tax twice. Employer National Insurance paid by the intermediary is not included in the set-off, and any penalties are still calculated on the full gross liability before the offset. For the set-off to apply, HMRC needs to identify the worker and the intermediary, and the deemed employer needs to supply the supporting information.