How to Challenge an IR35 Status Decision Without Friction

How to challenge an IR35 status decision without harming the client relationship

Disagreeing with a Status Determination Statement (SDS) does not have to mean a difficult conversation or a damaged working relationship. HMRC has set out a formal, client-led route for this, and understanding how it works helps contractors raise concerns calmly and professionally. This guide explains the IR35 status appeal process, how to go about disagreeing with an SDS politely, and what a contractor status dispute with a client typically involves in practice.

Why you might want to challenge an IR35 status decision

An SDS is the client's assessment of whether a contract falls inside or outside IR35. It should reflect the actual working practices: how much control the client exercises, whether a genuine right of substitution exists, and the wider picture of the engagement. Sometimes contractors feel the SDS does not match reality, perhaps because the written contract describes one arrangement but day-to-day working looks different.

It is worth remembering that the client, not the platform, not an accountant, and not HMRC's CEST tool on its own, is legally responsible for making this determination. CEST outputs are described by HMRC as not determinative, so a CEST result alone is not the end of the conversation. If something feels wrong, there is a structured way to challenge an IR35 status decision rather than simply accepting it or walking away from the contract.

The client-led disagreement process, step by step

HMRC guidance requires medium and large clients to run a client-led disagreement process for off-payroll working determinations. The mechanics are straightforward:

• The worker (or the deemed employer, such as a fee-payer agency) sets out which SDS they disagree with and their reasons.
• Representations can be made verbally or in writing, according to HMRC's employment status manual.
• The client must keep the worker's tax treatment unchanged while the disagreement is being considered.
• The client has 45 calendar days from receipt of the representations to respond.
• At the end of that period, the client must either confirm the original SDS and give reasons, or issue a new SDS if its view has changed.
• The client must keep records of the disagreement, as set out in HMRC's guidance on off-payroll working for medium and large clients.

This process sits within the client's own compliance obligations. Fee-payer responsibilities guidance confirms that the deemed employer carries parallel duties around tax treatment during a dispute, so agencies are often part of this conversation too.

Disagreeing with an SDS politely

The 45-day window and the written-reasons requirement exist precisely so this does not need to become adversarial. A few practical habits make the process smoother:

• Focus on facts, not conclusions. Rather than asserting "this should be outside IR35", describe the specific working practice that seems inconsistent with the SDS, for example how substitution would actually work in practice, or who directs the day-to-day method of work.
• Reference the right of substitution and control. Recent case law, including the Supreme Court's PGMOL decision, has sharpened focus on substitution and control as central status tests, rather than mutuality of obligation in isolation. Framing representations around these factors mirrors how HMRC and tribunals now approach status.
• Put it in writing. Even if an initial conversation is verbal, a written follow-up creates a clear record and starts the 45-day clock unambiguously.
• Keep it collaborative. The client is required to reconsider, not simply defend its original position. Presenting the disagreement as helping the client get the determination right, rather than as an accusation, tends to preserve the relationship.

What happens if the dispute is not resolved

If, after the client's review, the determination is still disputed, HMRC's internal manual notes that the matter can in principle go to the First-tier Tribunal. HMRC's own annual report also notes that options in disputed cases more broadly can include Alternative Dispute Resolution and statutory review mechanisms before matters reach litigation.

For general workplace disputes unrelated to the SDS process itself, such as treatment at work or contractual disagreements with an agency, GOV.UK signposts Acas, Citizens Advice, or a trade union for help and advice. Where the dispute touches on employment rights or status more broadly, the Fair Work Agency is the relevant regulator for enforcement matters, separate from HMRC's tax-focused SDS process.

Keeping the relationship intact

Clients generally do not enjoy status disputes any more than contractors do, particularly where a determination affects several engagements at once. Showing that you understand the client-led process, citing the correct 45-day timeframe, and grounding your representations in substitution and control rather than vague dissatisfaction all signal that you are engaging constructively rather than simply trying to force an outside-IR35 outcome.

It is also worth having a contract reviewed independently before raising a dispute, so representations are grounded in a specialist's reading of the actual clauses and working practices rather than assumption.

For contractors currently weighing up engagements, you can browse outside-IR35 contracts where the client states that determination, and compare terms using our day-rate benchmarks to understand how a given engagement sits in the current market.

This platform does not determine, verify, or warrant IR35 status; the SDS is the client's legal responsibility. Contractors should take their own advice and consider IR35 insurance.