IR35 (UK Off-Payroll Working Rules)

IR35 is the informal name for the UK’s off-payroll working rules, codified in Chapters 8 and 10 of Part 2 of the Income Tax (Earnings and Pensions) Act 2003 (ITEPA 2003). The rules target a long-standing structural mismatch in UK tax: a contractor working through their own limited company can pay materially less tax than an employee performing identical work for the same client, even when the relationship has all the features of employment. IR35 reclassifies the income in those engagements and forces PAYE and National Insurance to be operated as if the contractor were an employee.

How IR35 Works

IR35 applies when three elements are present: a worker, an intermediary (usually a personal service company), and a client to whom the worker provides services. If the engagement would be employment “but for” the intermediary, the rules apply. Status is assessed using employment-law indicators developed in case law: personal service and the right of substitution, mutuality of obligation, and the degree of control the client exercises over how, when, where, and what the worker does. Financial risk, integration into the business, and provision of equipment are secondary factors.

Two regimes coexist:

• Chapter 8 (the original IR35, since 2000). The intermediary self-assesses. If inside IR35, the intermediary must operate PAYE and NICs on a “deemed payment” calculated on the engagement income net of allowable expenses.
• Chapter 10 (off-payroll working). The end client determines status and the fee payer (usually the agency or client paying the intermediary) operates PAYE on inside payments. Chapter 10 applies to public bodies from April 6, 2017 and to medium and large private-sector clients from April 6, 2021, per HMRC’s off-payroll working guidance.

Under Chapter 10 the client must produce a Status Determination Statement (SDS), share it with the contractor and the contractual chain, and take reasonable care in reaching the determination.

Who Must Comply

• End clients that are public authorities, or medium or large private-sector entities engaging contractors through intermediaries
• Agencies and other fee payers in the supply chain to those clients
• Contractors operating through a personal service company that work for small private-sector clients (still under Chapter 8)
• Foreign companies with a UK presence (a UK permanent establishment, UK branch, or UK-resident connected company) engaging UK-based contractors

A small private-sector client is broadly an entity that does not meet two of three Companies Act 2006 tests in two consecutive financial years: turnover over GBP 10.2 million, balance-sheet total over GBP 5.1 million, more than 50 employees.

Status Determination Process

Per HMRC’s guidance for clients:

1. The client reviews the contract and the actual working practices.
2. The client uses HMRC’s CEST tool or another reasonable means to reach a determination.
3. The client issues a written SDS stating the conclusion and the reasons.
4. The SDS is passed down the chain to the fee payer.
5. The fee payer applies PAYE and NICs on inside payments.
6. If the contractor disagrees, they can invoke a 45-day client-led disagreement process.

Penalties

Penalties for IR35 failures sit under HMRC’s general tax penalty regime:

• Unpaid PAYE and NICs. The fee payer (or contractor under Chapter 8) is liable for the tax that should have been deducted, plus interest.
• Penalty for inaccuracy. Up to 30 percent of the lost revenue for careless errors, up to 70 percent for deliberate inaccuracy, up to 100 percent for deliberate and concealed.
• No reasonable care on SDS. Liability for the PAYE and NICs can transfer back to the client even where the fee payer would normally bear it.
• Reputational. Public bodies and listed companies face additional scrutiny over IR35 misclassifications.

Common Pitfalls

• Blanket inside-IR35 determinations. Issuing a single inside-IR35 SDS for every contractor without individual review is not reasonable care.
• Ignoring working practices. A contract that says “substitution allowed” but a working practice that forbids it is a working-practice case. HMRC and tribunals look at reality.
• Treating CEST as a defense without checking inputs. CEST stands behind the answers given. Bad inputs produce no protection.
• Missing the chain. Multiple intermediaries (umbrella, agency, PSC) require the SDS to be passed and absorbed all the way down.
• Forgetting Chapter 8 for small clients. A small private-sector client still drives a Chapter 8 obligation on the contractor’s PSC, which is often overlooked.

Related Forms and Terms

• EU Platform Work Directive: an EU analog regime focused on platform work rather than personal service companies.
• ABC Test: the dominant US worker-classification test, with structurally similar but legally distinct logic.
• Common Law Test for Worker Classification: the IRS-side US test that maps to many of the same facts CEST asks about.
• Permanent Establishment: a UK PE can pull a foreign company into Chapter 10 obligations.

Omnivoo Contract Management maintains UK engagement records, CEST inputs, and Status Determination Statements per contractor, with version history and reasonable-care evidence available to HMRC under inquiry.