IR35 and Off-Payroll Working: Rules, Risks and What to Do

If you work with contractors or plan to, IR35 (also called the off‑payroll working rules) needs to be on your radar. The rules can shift payroll tax responsibility onto the business paying for the work - and mistakes can be expensive.

Don’t stress - once you understand how IR35 works and put a clear process in place, you can confidently hire the talent you need while staying compliant.

In this guide, we explain IR35 from a small business perspective: when it applies, who’s responsible, how to assess contractor status, practical steps to reduce risk and the key documents you’ll want in place.

What Is IR35 And Why Does It Matter To Your Business?

IR35 is the UK’s “off‑payroll working” regime. In plain English, it’s designed to catch arrangements where an individual provides services through their own limited company (often called a “personal service company” or PSC), but for all intents and purposes would be an employee if you looked at the working relationship without that company in the middle.

IR35 sits in the Income Tax (Earnings and Pensions) Act 2003 (ITEPA) and was reformed in April 2021 for the private sector (public sector rules changed in 2017). Under those reforms, the responsibility for deciding whether IR35 applies - and for operating PAYE and National Insurance (NI) where it does - moved in many cases from the contractor’s PSC to the business that engages them (the “client”) or another party in the supply chain (the “fee‑payer”).

Why it matters to you:

• If IR35 applies and you’re the fee‑payer, you must deduct PAYE, employee NI and potentially the Apprenticeship Levy, and pay employer NI - as if the individual were on payroll (but they’re still not an employee for employment law by default).
• Get it wrong, and HMRC can pursue unpaid tax, NI, interest and penalties - often for multiple tax years.
• IR35 influences your hiring model, budget (gross vs net cost of labour), contracts, and day‑to‑day management of contractors.

Who Decides IR35 Applies? The Small Business Exemption Explained

In the private sector, who makes the IR35 decision depends on your size:

• Small businesses: If you qualify as “small” for Companies Act purposes (meeting two of these: turnover ≤ £10.2m, balance sheet total ≤ £5.1m, ≤ 50 employees), the responsibility stays with the contractor’s PSC. You still want robust contracts and sensible practices, but you’re generally not the party operating PAYE.
• Medium or large businesses: You (the client) must assess IR35 for each engagement, issue a Status Determination Statement (SDS), take “reasonable care,” and ensure the fee‑payer (often you, sometimes an agency) deducts PAYE and NI when the engagement is inside IR35.

If you sit in a group structure, the size test applies to the group. If you’re unsure about your size status, get tailored advice - responsibility can move based on how your business grows.

How To Assess Employment Status For IR35

IR35 decisions turn on employment status in tax law: would the contractor be an employee if you ignored the PSC? There’s no single tick‑box. HMRC and case law look at the overall picture. Three core factors often carry the most weight:

1) Personal Service And Substitution

Is there an unfettered right to send a genuine, suitable substitute - and does that happen in practice? A genuine right of substitution points away from employment. If your work requires the individual’s personal service and you wouldn’t accept a substitute, that leans towards employment.

2) Control

Who decides what work is done, how, when and where? High levels of client control (set hours, close supervision, approval of methods) suggest employment. A contractor who sets their own schedule and method and focuses on deliverables looks more like a business on their own account.

3) Mutuality Of Obligation (MOO)

Are you obliged to provide ongoing work, and is the contractor obliged to accept it? Open‑ended, continuous obligations point to employment; project‑based or intermittent engagements with the freedom to refuse work point to self‑employment.

Other indicators matter too:

• Financial risk (e.g. fixed‑price projects, rectifying defective work at their own cost)
• Provision of equipment and tools
• Integration into your organisation (using your email domain, being on org charts, managing your staff)
• Ability to work for others concurrently
• How payment is structured (day rate vs milestones, invoices vs payroll)

Useful resources and actions:

• Map the role against recognised employment status tests and document your reasoning.
• Use HMRC’s CEST tool as one input, but don’t rely on it blindly - ensure your answers reflect real‑world practices and your contract terms.
• Sense‑check the engagement against your internal policies and risk appetite. If the facts look like employment, consider an Employment Contract instead.

Inside vs Outside IR35: What Changes For Payroll And Contracts?

If The Engagement Is Inside IR35

Where your SDS concludes IR35 applies (and you’re the fee‑payer):

• Operate PAYE on the “deemed direct payment” (subject to tax and NI), pay employer NI and account for the Apprenticeship Levy if applicable.
• Adjust day rates to reflect employer costs, budget impacts and the fact the contractor can no longer offset expenses in the same way via their PSC.
• Issue the SDS to the contractor and any agency, and have a client‑led disagreement process to respond within 45 days if challenged.
• Update contracts to reflect off‑payroll deductions and responsibilities, and ensure indemnities and warranties align with the tax position.

If The Engagement Is Outside IR35

When the working practices and contract support genuine self‑employment:

• Make sure your Contractor Agreement matches reality (e.g. substitution rights, deliverables‑focused scope, limited control and integration).
• Review project‑based scopes and change control mechanics so the contractor operates as a business in their own right (invoicing, tools, insurance).
• Avoid “drift” in practices over time (e.g. setting fixed hours or giving line‑management duties) that could move the engagement inside IR35 in substance.

Note: An “inside IR35” finding for tax does not automatically confer employee rights under employment law. However, the same factors are often analysed in both contexts, so it’s wise to sense‑check the risk of employment claims and consider whether the role should in fact be employed.

Practical Steps To Manage IR35 Risk In A Small Business

1) Build An IR35 Process

Have a clear, documented workflow:

• Pre‑engagement triage (do we need a contractor or employee?).
• Status assessment with documented reasoning and sign‑off.
• Issuing the SDS (where applicable) and handling disagreements.
• Contract drafting aligned to the assessment.
• Onboarding with guidance on working practices to match the status.
• Periodic review (particularly if scopes change or the engagement becomes long‑term).

2) Use Robust, Aligned Contracts

Contracts won’t save an “employment‑like” relationship, but they’re critical to set expectations and support your assessment. Consider:

• A well‑drafted Contractor Agreement with a genuine substitution clause, clear deliverables, IP and confidentiality provisions, and appropriate risk allocation.
• If there’s a supply chain, a matching Sub‑Contractor Agreement to keep terms consistent down the line.
• Where the role actually looks like employment, switch to an Employment Contract and on‑payroll engagement.

3) Match Working Practices To Your Decision

Align day‑to‑day realities with your IR35 outcome:

• Outside IR35: let contractors control methods and scheduling where possible, accept substitutes, avoid putting them into employee‑style performance or disciplinary processes.
• Inside IR35: operate PAYE correctly, and be realistic about control and integration - if you want to treat someone like staff, employment may be the cleaner option.

4) Keep Evidence And Take “Reasonable Care”

HMRC expects “reasonable care” when you issue an SDS. Keep a file: job description, assessment notes, CEST output, contract, emails confirming substitution acceptance, and periodic reviews. If challenged, this paper trail really helps.

5) Plan For Alternatives

Depending on your needs, consider other models:

• Umbrella company (the individual is employed by the umbrella; you contract with the umbrella).
• Statement of work (SOW) with fixed deliverables and milestones to emphasise project‑based outcomes.
• Engaging suppliers overseas where appropriate - though you still need to consider UK overseas contractors issues, tax nexus and data protection.

IR35 And Your Wider Employment Law Strategy

IR35 is a tax framework, but it sits alongside employment law considerations. If a contractor is closely integrated and managed like staff, you may face status challenges beyond tax (e.g. claims for worker rights like holiday pay). To reduce risk, make sure your broader people strategy is consistent.

• Be clear on worker vs employee vs self‑employed categories.
• If you truly need an employee for stability and control, hire with an Employment Contract and bring them onto payroll.
• Where you need flexible capacity for defined deliverables, structure a genuine business‑to‑business engagement using a strong Contractor Agreement.
• If you rely on a layered supply chain, ensure the contractor vs subcontractor split is clear and risk‑aligned.

Finally, think ahead about post‑engagement restrictions and confidentiality. If you need to protect clients, pipelines or IP when a contractor moves on, ensure your covenants are tailored and reasonable - the same drafting disciplines you’d use for non‑compete clauses in employment can inform contractor restrictions too (appropriately adapted).

Common IR35 Pitfalls (And How To Avoid Them)

“Contract Says One Thing, Reality Says Another”

HMRC looks at working practices. If your contract gives a substitution right but you’d never accept a substitute in practice, that right won’t carry much weight. Align reality with paper - or change the paper to reflect reality.

Status Drift Over Time

Engagements that start as short, deliverables‑based projects can morph into day‑rate, long‑term roles with fixed hours and integrated management. Schedule periodic reviews (for example, every three months) to see whether your “outside IR35” rationale still stacks up.

No SDS Trail Or Reasonable Care

For medium/large clients, failure to take reasonable care with the SDS can make you liable even if you pass payment to an agency. Keep an audit trail and confirm the SDS travels down the chain.

Using Day Rates Like Payroll

Paying a single day rate, dictating fixed hours and approving timesheets like an employee system are classic risk flags. If you need that level of control, bring the role inside IR35 (or onto payroll) and budget accordingly.

Ignoring Agency Chains

In multi‑party chains, the “fee‑payer” is the entity that pays the PSC. Make sure contracts and SDSs identify who is fee‑payer, and build in warranties and indemnities that reflect each party’s role.

What To Include In Your Contractor And Off‑Payroll Documents

Strong documents won’t override an employment‑like relationship, but they help articulate expectations and reduce risk. Depending on your model, consider:

For Outside IR35 Engagements

• Contractor Agreement (unfettered substitution, deliverables‑led scope, limited control, own equipment, insurances, ability to work for others, milestone or project pricing, change control)
• Sub‑Contractor Agreement (if your contractor engages others)
• IP ownership and licence terms tailored to your business (who owns the outputs and when)
• Confidentiality and data protection obligations proportionate to access

For Inside IR35 Engagements

• Off‑payroll addendum confirming PAYE/NI deductions on deemed payment, VAT handling, and clarity on benefits (generally none) and policies that do or do not apply
• Clear deliverables, termination rights and liability caps reflecting the commercial risk
• Agency contracts aligning SDS responsibilities and fee‑payer obligations in the chain

If you decide the role should be employed, use a tailored Employment Contract instead and bring the individual fully inside your HR framework (including policies, handbooks and benefits).

Frequently Asked IR35 Questions From Small Businesses

Do We Still Pay VAT To A PSC If The Role Is Inside IR35?

Typically yes - VAT is still chargeable by a VAT‑registered PSC on the invoice for services. The fee‑payer calculates PAYE/NI on the “deemed direct payment,” but VAT (if applicable) is still paid to the PSC on top.

Does An Inside IR35 Contractor Become Our Employee?

No - IR35 is a tax concept. However, the same factual matrix can lead to employment or “worker” status claims, so sense‑check whether employment would be cleaner if you want long‑term control and integration.

Can We Use CEST And Be Safe?

Use CEST as a tool, not a shield. HMRC expects “reasonable care,” which includes accurate inputs and alignment between contract terms and working practices. Keep evidence of your assessment and revisit it if the engagement changes.

We’re A Small Company - Do The 2021 Rules Affect Us?

If you’re small under Companies Act thresholds, the responsibility to assess generally remains with the contractor’s PSC. You should still contract sensibly and manage working practices, but you’re not usually the fee‑payer for IR35 purposes unless you grow beyond “small.”

What If We Work With Overseas Contractors?

IR35 applies where there’s a UK connection to the engagement and supply chain, but international setups add complexity (tax residency, PE risk, data transfers). If you’re engaging talent abroad, review the arrangement alongside overseas contractor considerations and tailor your contracts accordingly.

Key Takeaways

• IR35 is about employment status for tax. If a contractor looks and works like an employee, the off‑payroll rules can make you (or an agency) responsible for PAYE and NI.
• Small private sector clients leave the decision with the contractor’s PSC; medium and large clients must assess, issue an SDS, take reasonable care and ensure deductions are made when inside IR35.
• Base your assessment on substitution, control and mutuality of obligation, supported by the overall picture, and keep an evidence file for each engagement.
• Align contracts and working practices to your decision. Where the role is genuinely independent, use a clear, tailored Contractor Agreement; where you need control and long‑term integration, consider an Employment Contract.
• Review engagements periodically - status can drift over time as scopes, hours and management change.
• Don’t rely solely on templates or CEST outputs. Getting the structure and documentation right early will reduce your tax exposure and help you hire with confidence.

If you’d like help building an IR35‑ready hiring process, drafting a Contractor Agreement or deciding when to put someone on payroll, our team can help. You can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no‑obligations chat.