IR35 Off-Payroll Working Rules for the Private Sector

The IR35 off-payroll working rules tax contractors who provide services through an intermediary (typically a Personal Service Company) as if they were employed by the end client. The April 2021 private sector reform shifted responsibility for determining status from contractors to medium and large clients. This guide explains how the rules work and what contractors and hirers need to know.

1. IR35 Overview

IR35 is the shorthand name for the off-payroll working rules, which were first introduced in 2000. The rules are now found in ss.61A–61Z5 of the Income Tax (Earnings and Pensions) Act 2003 (ITEPA 2003), significantly expanded by the Finance Acts of 2017 (public sector reform) and 2021 (private sector reform).

The purpose of IR35 is to ensure that contractors who would be employees if they contracted directly with the client — rather than through an intermediary such as a Personal Service Company (PSC) — pay broadly the same income tax and National Insurance as a direct employee. Without IR35, a contractor can take income as dividends, avoiding National Insurance and paying a lower dividend tax rate.

The rules apply where:

• A worker provides services to a client through an intermediary (usually a PSC)
• If the worker had contracted directly with the client, they would be regarded as an employee for tax purposes
• The circumstances of the engagement meet the deemed employment tests (see section 4)

2. Who Determines Status — Client vs Contractor

The critical change in the April 2021 reform was shifting responsibility for status determinations:

Where the end client determines status, they must issue a Status Determination Statement (SDS) to the agency and contractor, and the fee-payer (the party in the supply chain that pays the PSC) must operate PAYE and NI deductions on inside-IR35 payments. The liability passes through the supply chain: if the client fails to issue an SDS, the liability falls on the client; if the agency fails to pass on the SDS, liability may shift to the agency.

3. Small Company Exemption

Small private sector clients are exempt from the April 2021 responsibility shift. For this purpose, a "small" client is one that meets the Companies Act 2006 small company definition: satisfying at least 2 of the following 3 conditions in the most recent financial year:

• Annual turnover no more than £10.2 million
• Balance sheet total no more than £5.1 million
• No more than 50 employees

Where the client qualifies as small, the contractor's PSC is responsible for determining its own IR35 status (as under the original 2000 rules). The PSC must apply the same employment status tests and, if caught, operate the deemed employment payment calculation and account for PAYE and NI itself.

Note: the small company test looks at the client's own accounts. Sole traders and unincorporated businesses that are not "companies" are not automatically exempt — HMRC's position is that unincorporated businesses are caught by the general rules regardless of size, though in practice HMRC applies the same conditions by analogy.

4. The IR35 Tests — Employment Status Factors

The IR35 determination uses the employment status tests developed through decades of case law. No single factor is determinative — HMRC and tribunals consider the whole picture of the working relationship. Key tests:

1. Substitution — does the contractor have a genuine, unconditional right to send a substitute to perform the work? If the client must accept any suitably qualified substitute (and the right has been or would realistically be exercised), this strongly points to outside IR35. A substitution clause in a contract that the client would never accept in practice carries very little weight.
2. Control — does the client control how the work is done, not just what is delivered? High control (set working hours, prescribed methods, daily supervision) points towards employment. Low control (contractor decides how, when, and where to work) points outside IR35.
3. Mutuality of Obligation (MOO) — is the client obliged to offer work, and is the contractor obliged to accept it? Ongoing obligation between projects points towards employment. Project-by-project engagement with no guarantee of further work points outside.
4. Financial risk — does the contractor bear genuine financial risk (e.g. fixed-price contracts where inefficiency leads to loss, or responsibility for rectifying defects at own cost)? Pure time-and-materials engagements with no financial risk point towards employment.
5. Equipment— does the contractor provide their own significant equipment? Using the client's equipment, premises, and systems points towards employment; providing specialist equipment or software points outside.
6. Part and parcel— is the contractor integrated into the client's organisation (attending staff meetings, on internal directories, receiving employee benefits)? High integration points inside IR35.

5. Status Determination Statement

Medium and large clients must issue a Status Determination Statement (SDS) before or when the engagement begins. The SDS must:

• State whether the engagement falls inside or outside IR35
• Give the reasons for the determination, with reference to the specific factors considered
• Be passed to the agency (if applicable) and to the worker

Disagreement right (45-day rule): Contractors have the right to disagree with the SDS within 45 days of receiving it. The client must acknowledge receipt and respond within 45 days, either upholding or revising the determination. If the client fails to respond within 45 days, the determination is treated as not having been made — and liability passes back to the client.

A blanket determination that all contractors are inside IR35 without individual assessment is unlawful and may itself create liabilities. HMRC expects each engagement to be assessed on its specific facts.

6. The CEST Tool

HMRC's Check Employment Status for Tax (CEST)is a free online tool that asks a series of questions about the engagement and produces an inside, outside, or "undetermined" result. HMRC has committed to standing behind CEST results where information is entered accurately and in good faith.

CEST limitations widely acknowledged by tax professionals:

• CEST does not directly test mutuality of obligation — a significant gap given that MOO is a fundamental employment status test in case law (e.g. Autoclenz v Belcher [2011] UKSC 41)
• CEST returns "undetermined" in a significant proportion of cases, providing no guidance
• The tool cannot properly assess nuanced or complex arrangements
• Multiple IR35 cases (including RALC Consulting, Kickabout Productions) have gone against what CEST would have indicated

CEST can be used as one input in a broader status assessment but should not be relied upon exclusively for high-value or long-running engagements.

7. Inside IR35 — Deemed Employment Payment

Where an engagement is determined to be inside IR35, the fee-payer in the supply chain must:

• Deduct income tax (PAYE) and employee's National Insurance (12% up to UEL; 2% above) from payments to the PSC
• Pay employer's National Insurance (13.8%) on top of the payment
• Account for these amounts to HMRC via RTI

The PSC receives the gross fee less the PAYE and NIC deductions. The contractor can then pay themselves from the PSC, but because the income has already been taxed at employment rates, there is little tax advantage to operating through a PSC for that engagement.

Note: the contractor does notreceive employment rights (such as holiday pay, sick pay, redundancy pay, or pension auto-enrolment rights) simply because they are taxed as a deemed employee. This "worker without rights" status is one of the most criticised aspects of the IR35 regime.

8. Umbrella Company Route

Some contractors — particularly those whose engagements are inside IR35 or who want to avoid IR35 complexity — choose to work through an umbrella company, which employs them on a PAYE basis and invoices the agency or end client.

Compliant umbrella companies:

• Employ the contractor and operate PAYE and NI in full
• Pass on the employment costs (employer NI, holiday pay, apprenticeship levy) which reduce the contractor's take-home pay
• Should be members of the FCSA (Freelancer and Contractor Services Association) or Professional Passport accreditation schemes

Non-compliant umbrella companies and disguised remuneration:

• Schemes promising take-home rates of 85%+ are almost invariably non-compliant. There is no legitimate way to achieve such rates while paying the full employment taxes legally due.
• Most such schemes involve disguised remuneration — paying contractors through loans, grants, or other non-employment vehicles that HMRC does not recognise as tax-free. The Loan Charge legislation has retrospectively taxed many of these arrangements, with devastating consequences for contractors who used them in good faith.
• HMRC publishes a list of known non-compliant schemes and operates a hotline for reporting them.

9. Genuine Outside IR35 — What Works

To successfully operate outside IR35, both the contract and working practice must demonstrate that the engagement is not one of employment. The factors below are particularly important:

• Substitution that works in practice — the contract should grant an unconditional right to substitute; the clause must be commercially realistic; and ideally there should be evidence that the right has been exercised (even partially). Courts have dismissed substitution clauses that are clearly not genuine.
• Working practice alignment — the way the engagement operates day-to-day must match the contract terms. Setting your own hours, working from your own premises, providing your own equipment, working for multiple clients simultaneously, and being paid for deliverables rather than time all support outside IR35.
• Multiple clients — working for several clients simultaneously is a strong indicator of genuine business operation rather than disguised employment.
• Fixed-price contracts — agreeing to deliver a defined output for a fixed price (with financial risk if the work takes longer than expected) strongly points outside IR35.
• Professional tax advice — contractors operating outside IR35 should take specialist advice and maintain a file of evidence supporting the determination, including the contract, client correspondence, and a contemporaneous record of working practices.

10. Penalties — Historic Liability and Investigations

HMRC has significant powers to investigate and recover unpaid tax from IR35 non-compliance, including for historic periods:

• Discovery assessments — HMRC can raise assessments going back 4 years for careless errors, 6 years for deliberate errors (or where the taxpayer has failed to notify chargeability), and in theory up to 20 years in cases of deliberate concealment
• Tax-geared penalties under Schedule 24 Finance Act 2007: 30% of tax for careless behaviour; 70% for deliberate (not concealed); 100% for deliberate and concealed. Reductions apply for prompted and unprompted disclosure.
• Interest — HMRC charges interest at the official late payment rate (currently 7.5%+ per year) on all underpaid tax from the date it was due
• HMRC Connect and data matching — HMRC uses its Connect system and data from HMRC RTI, Companies House, Land Registry, and foreign tax authorities to identify contractors who may have incorrectly operated outside IR35

Contractors facing HMRC investigations should seek specialist representation immediately. Early voluntary disclosure and settlement discussions with HMRC typically result in significantly reduced penalties and can prevent the escalation to formal tribunal proceedings.