IR35 Assessment: Check Contractor Status And Reduce Risk In The UK

If you hire contractors (especially for IT, marketing, design, construction, consultancy, or project work), IR35 can feel like one of those “we’ll deal with it later” issues.

But the reality is: carrying out an IR35 assessment is one of the most important risk checks you can run before you onboard a contractor, renew an engagement, or change someone’s day-to-day working arrangements.

Done properly, IR35 doesn’t have to be scary. It’s really about one core question: is your contractor genuinely independent, or are they working like an employee in practice?

In this guide, we’ll walk you through what IR35 means for small UK businesses, how to carry out a practical IR35 assessment, what evidence you should keep, and how to reduce the risk of tax and employment disputes down the track. This article is general information only and isn’t tax advice - IR35 can be fact-specific, so consider getting tailored tax/accounting advice for your situation.

What Is IR35 (Off-Payroll Working) And Why Should Your Business Care?

IR35 is shorthand for the UK’s “off-payroll working” rules. These rules are designed to stop “disguised employment” - where an individual works like an employee but provides their services through an intermediary (often a personal service company).

From a small business perspective, IR35 matters because if a contractor is effectively an employee for tax purposes, someone in the chain can end up liable for:

• Income Tax that should have been deducted
• National Insurance Contributions (NICs)
• Interest and penalties if the position is challenged later

Who pays (and who is liable) depends on the off-payroll rules and your circumstances. In many private-sector cases, the key roles are:

• Client (your business): determines status (inside or outside IR35) where the off-payroll working rules apply to you
• Fee payer (often the business paying the PSC, sometimes an agency): is responsible for operating PAYE and NICs if the engagement is inside IR35

And it’s not just tax. If someone looks and behaves like an employee, you can also face practical employment-law risks (for example, claims that they’re entitled to holiday pay or other worker protections).

That’s why an IR35 assessment shouldn’t be a “tick-box” exercise. It’s part of your legal foundations - getting the relationship right from day one, so you can scale without nasty surprises.

Does IR35 Apply To Every Contractor?

No. IR35 typically becomes relevant when an individual supplies services via an intermediary (commonly a personal service company), and the working arrangement could be considered employment-like.

Also, the off-payroll working rules don’t apply in the same way to every business. For many small private-sector clients, the responsibility to determine status may sit with the contractor’s intermediary rather than the client (though you can still have wider tax and employment-status risks if the arrangement is employee-like in practice). Because the “small company” position and supply chains can be technical, it’s worth confirming where responsibilities sit in your specific set-up.

However, even where IR35 doesn’t strictly apply, the underlying question still matters: what is the contractor’s true status? Getting this wrong can cause contract disputes, tax confusion, and management headaches.

If you need a refresher on the broader landscape of status, it’s worth being clear on the differences between employee, worker and self-employed contractor - because those distinctions tend to show up in IR35 discussions as well. Having a baseline understanding of employment status can make your assessment much more consistent.

When Should You Carry Out An IR35 Assessment?

In most small businesses, IR35 risk creeps in when contractor relationships become long-running or “business as usual”.

As a rule of thumb, you should run an IR35 assessment:

• Before onboarding a new contractor (or before signing the contract)
• When renewing a contractor engagement, extending a term, or changing the scope
• When the working arrangement changes (e.g. they start managing staff, shift to set hours, or become embedded in your team)
• If the contractor disputes their status or asks to be treated differently (e.g. wants employee-like benefits)
• Before a funding round or sale where due diligence might scrutinise contractor arrangements

Even if you’ve “always used contractors”, that doesn’t guarantee your current structure is low-risk. Often the risk comes from informal day-to-day practices rather than what the paperwork says.

Small Businesses Often Ask: “Do We Even Count Under IR35 Rules?”

IR35 responsibilities can differ depending on factors like the size of the organisation and the nature of the intermediary arrangement.

In the private sector, whether your business is classed as “small” can affect who has to make the status determination and issue the status decision statement (SDS). If you’re not “small” (for example, you meet the relevant company-size tests), you’ll generally be expected to make the determination and communicate it. If you are “small”, the responsibility may instead sit with the contractor’s intermediary.

Because the off-payroll rules can be technical (and the practical stakes can be high), it’s smart to treat IR35 as a structured risk check rather than a vague “HR thing”. If you’re unsure where your business sits, getting tailored advice early can save a lot of time and cost later.

How To Run A Practical IR35 Assessment (Step-By-Step)

A useful IR35 assessment looks at both:

• The written contract (what the parties agreed), and
• The reality on the ground (how the work is actually performed)

Here’s a practical step-by-step approach you can use internally.

1) Confirm Who You’re Engaging (And Through What Structure)

Start with the basics:

• Are you contracting with an individual directly?
• Or with a limited company / intermediary?
• Who invoices you, and who is named in the agreement?

This matters because IR35 is fundamentally about situations where an intermediary is used, and the individual could be classed as an employee if the intermediary didn’t exist.

2) Map The Role And Deliverables (Not Just “Hours Worked”)

A common IR35 trap is describing the engagement like an employment job description.

Instead, document:

• The project scope (what outcome you’re buying)
• Deliverables (what “done” looks like)
• How success is measured
• Any milestones and timelines

When your agreements are structured around deliverables and outcomes, it’s often easier to show the contractor is genuinely operating a business in their own right.

3) Work Through The Core Status Factors

In most IR35 assessments, the following factors carry a lot of weight:

• Control: Do you control how, when, and where the contractor works - or do you mainly control the final output?
• Substitution / personal service: Does the contractor have a genuine right to send a substitute (and would you accept one in practice)?
• Mutuality of obligation: Are you obliged to offer ongoing work, and is the contractor obliged to accept it?
• Integration: Are they embedded into your team like staff (company email, org chart, managing employees, attending internal meetings as “one of you”)?
• Financial risk: Can they make a loss, quote fixed fees, correct defective work at their own cost, or invest in their own tools?

No single factor automatically decides the outcome every time. The point is to build a clear picture of whether this looks like a contractor relationship or employment in disguise.

4) Record Your Outcome (And The Reasons)

An IR35 assessment is much more defensible when you keep written records of:

• the outcome you reached (inside / outside IR35), and
• the specific facts you relied on to reach that decision

This record is incredibly helpful if the relationship is questioned later - whether by HMRC, by auditors in due diligence, or by the contractor themselves.

5) Align Your Contracts With The Reality

Once you’ve assessed the working relationship, your next step is making sure your documentation supports it.

For example, if the reality is that the contractor has flexibility and autonomy, but the contract reads like an employment agreement (fixed hours, strict reporting lines, “manager approval for leave”), that mismatch can create risk.

Strong contractor documentation isn’t just about “having a contract” - it’s about having one that matches the way you actually work together. If you’re engaging contractors regularly, putting the right Contractors Agreement in place can reduce ambiguity and help set expectations on both sides.

What Evidence Should You Keep To Support Your IR35 Assessment?

If your business is ever challenged on a contractor’s status, the question won’t just be “what did your contract say?” It will be “what actually happened?”

So alongside the contract, you’ll want a practical paper trail showing the contractor is genuinely independent.

Helpful Evidence To Keep On File

• Signed contract and any variations (including scope changes)
• Invoices and payment records (showing project fees, milestones, or agreed rates)
• Statements of work and deliverables
• Proof they work for other clients (where appropriate and available)
• Evidence of autonomy (e.g. they set their own hours, choose their own tools, or work offsite)
• Evidence of financial risk (e.g. fixed price projects, rework at their cost, their own insurance)
• Internal notes of your IR35 assessment and the reasons for your conclusion

Don’t Forget: A Contract Needs To Be Enforceable

It sounds obvious, but it’s worth stating: if your documentation is vague, inconsistent, or doesn’t reflect how you actually operate, it can be hard to rely on when things go wrong.

If you want to sanity-check whether your paperwork is structured properly, it helps to understand what makes a contract legally binding - because enforceability issues can undermine even a well-intentioned IR35 approach.

Common IR35 “Red Flags” For Small Businesses (And How To Fix Them)

Most IR35 problems we see in small businesses aren’t deliberate. They happen because:

• a contractor “just becomes part of the team”, or
• the business grows quickly and processes don’t keep up

Here are some common red flags - and practical fixes that can help reduce risk.

Red Flag 1: You Treat Contractors Like Employees Day-To-Day

Examples: approving “leave”, setting rotas, requiring attendance at recurring internal meetings, or managing them through the same performance processes as staff.

Fix: manage contractors through scope, deliverables, and timelines rather than staff-style supervision. Where they do need to coordinate with your team, keep it focused on project outcomes.

Red Flag 2: The Engagement Is Open-Ended With No Clear Deliverables

Examples: “ongoing support” with no defined outputs, or rolling month-to-month arrangements that mirror permanent roles.

Fix: use a statement of work or project-based schedule that clearly sets out what the contractor is delivering, and when.

Red Flag 3: Your Contract Says “Contractor”, But Your Practices Say “Employee”

This mismatch is a big risk area. If your agreement includes contractor-friendly clauses, but your managers operate as though they can direct the contractor like staff, you’re undermining your own position.

Fix: train the people who actually manage contractors. The “working practices” side of an IR35 assessment is often where businesses slip up, not the paperwork.

Red Flag 4: You Don’t Have Clear Commercial Terms

If your contractor engagements are inconsistent (different rates, unclear payment terms, no defined scope), it’s harder to show a clean, business-to-business relationship.

Fix: standardise your onboarding and commercial terms. For many small businesses, having clear Terms and Conditions for services and procurement processes can help create consistency - even if you still tailor the scope for each project.

How To Reduce IR35 Risk In Your Business Long-Term

An IR35 assessment is not a one-off document you file away and forget. The safest approach is to build a repeatable process that stays aligned as your business grows.

Build An “IR35-Friendly” Contractor Onboarding Process

When you hire your first few contractors, it’s tempting to move quickly and “sort the paperwork later”. But IR35 is exactly the kind of area where early foundations matter.

A simple onboarding checklist might include:

• Confirm the contractor’s contracting entity (individual vs company)
• Run your IR35 assessment and record the decision
• Sign the right contract before work begins
• Define deliverables and milestones
• Assign an internal point of contact (without turning it into line management)

Review Status When The Role Changes

IR35 risk increases when contractors become “key people” in your operations.

For example, imagine you bring in a contractor for a short systems project. It goes well, so you keep extending them. Six months later they’re managing your internal staff, working set hours, and attending all-hands meetings.

Even if the original engagement was low-risk, those day-to-day changes can shift the outcome of an IR35 assessment.

Keep Contractor Arrangements Separate From Employment Processes

If you have employees as well as contractors, it’s important not to blur the lines between them.

In practice, that means:

• Employees should be on an Employment Contract, with clear policies and entitlements.
• Contractors should be engaged under a contractor agreement, paid against invoices, and managed through deliverables.

This separation isn’t about being harsh - it’s about being clear and consistent, which protects your business and reduces misunderstandings.

Don’t DIY Complex Arrangements (Especially Where The Role Looks Like A “Core Function”)

If a contractor is effectively filling a role that looks like a permanent job (or you’re replacing an employee with a contractor), you’re in higher-risk territory.

That’s when it’s worth getting advice on the structure, the contract wording, and the way the engagement is run in practice. The cost of doing it properly upfront is usually far less than the cost of fixing it later.

Key Takeaways

• An IR35 assessment helps you determine whether a contractor engagement looks like genuine self-employment or disguised employment for tax purposes.
• For small businesses, the biggest IR35 risks usually come from day-to-day working practices (control, integration, ongoing obligations) rather than the contract alone.
• A practical IR35 assessment should be documented, including the facts you relied on and the reasons for your decision.
• To reduce long-term risk, build a repeatable contractor onboarding process, keep contractor arrangements separate from employment processes, and review status when the role changes.
• Well-drafted contracts matter - but they need to reflect reality. If your contractor agreements read like employment contracts (or your managers treat contractors like staff), you’re increasing risk.

If you’d like help reviewing your contractor arrangements or putting the right agreements in place, you can reach us at 08081347754 or team@sprintlaw.co.uk.