IR35 Rules: What UK Businesses Must Know When Hiring Contractors

Hiring contractors can be a smart way to scale your business quickly, access specialist skills, and keep overheads lean.

But if you’re not careful, contractor arrangements can also create unexpected tax risk - especially under IR35 (often called the “off-payroll working rules”).

This guide explains the IR35 rules for small UK businesses that engage contractors, consultants, freelancers, and project-based workers. We’ll break down what IR35 is, why it matters, how status is assessed, and what practical steps you should take so you can hire with confidence.

What Are IR35 Rules (And Why Do They Exist)?

IR35 is a set of UK tax rules designed to stop “disguised employment”. In simple terms, it targets situations where someone works like an employee, but is paid like a contractor - typically through an intermediary such as a personal service company (PSC).

The concern from HMRC is that, if the relationship looks like employment in practice, the worker may be paying less tax and National Insurance than they would as an employee, and the engager may be avoiding employer National Insurance and employment obligations.

So, when people talk about “understanding IR35”, what they’re really asking is:

• When does a contractor relationship get treated like employment for tax purposes?
• Who has to decide the status?
• Who carries the risk if HMRC disagrees?

IR35 doesn’t ban using contractors. It just means you need to get the status right and structure the engagement properly from day one.

What Counts As “Inside IR35” vs “Outside IR35”?

These are common phrases you’ll hear:

• Inside IR35 generally means the contractor is treated like an employee for tax purposes (even if they’re not legally an employee). Under the off-payroll rules, the party that pays the contractor’s intermediary (the “fee-payer”) may need to make PAYE-style deductions and account for employer National Insurance (depending on how the chain is structured).
• Outside IR35 generally means it’s a genuine business-to-business service relationship, and the contractor remains responsible for their own tax arrangements (again, depending on the structure and who pays whom).

It’s worth noting: IR35 status is about tax treatment and working arrangements - it’s not exactly the same as employment law status. But in practice, the tests overlap a lot, and getting either wrong can cause real headaches.

Why IR35 Matters For Small Businesses Hiring Contractors

For many SMEs, the biggest risk with IR35 isn’t “getting in trouble” for using contractors - it’s the cost and disruption of getting status wrong.

If HMRC later decides an engagement should have been treated as employment for tax purposes, this can lead to:

• Tax and National Insurance liabilities (sometimes going back years)
• Interest and penalties
• Admin burden responding to HMRC queries and producing documentation
• Commercial disputes with the contractor (especially if your contract says one thing but your day-to-day reality says another)
• Wider legal risk, because if someone is effectively treated like staff, they may also start raising employment law arguments (holiday pay, unfair dismissal, etc.)

Even if you’re a small business, IR35 can still apply. The “who decides status” and “who carries the liability” depends on factors such as the contractor’s structure (for example, PSC vs sole trader) and whether the engager is “small” under the off-payroll working rules.

As a starting point, a company is generally “small” if it meets at least two of these conditions: turnover of not more than £10.2m, balance sheet total of not more than £5.1m, and not more than 50 employees (with related rules for groups and connected entities). If the engager is “small”, the off-payroll rules typically do not require the engager to issue an IR35 status determination; instead, the contractor’s intermediary (such as the PSC) usually remains responsible for assessing IR35 and accounting for tax.

Practically, the safest approach is to:

• consider IR35 status before work starts,
• document your reasoning, and
• make sure your contract and real-world practices match.

This is also why it’s helpful to be clear on general employment status concepts - the same themes show up again and again in IR35 discussions.

How Do You Determine If A Contractor Is Inside Or Outside IR35?

There isn’t one single “magic” factor that decides IR35. HMRC and the courts look at the reality of the working relationship.

That said, a few key themes come up consistently. If you want a working-level understanding of IR35, start here.

1) Control: Who Decides How The Work Is Done?

Control looks at things like:

• Do you decide the contractor’s working hours and location?
• Do you closely supervise the work like you would an employee?
• Is the contractor told how to do the job, or just what outcome is required?

Contractors can still be directed on deliverables and deadlines - that’s normal in a commercial project. The risk increases when the contractor is managed like part of your internal team, with day-to-day instruction and little autonomy.

2) Substitution: Can The Contractor Send Someone Else?

A genuine contractor business often has the ability to provide a substitute (another suitably qualified person) to perform the services.

If the arrangement is very personal (you’ve hired that individual and no one else is acceptable), that points more towards employment-like characteristics.

Substitution clauses need to be real, not just words in a contract. If in practice you’d never allow a substitute, HMRC may give little weight to it.

3) Mutuality Of Obligation: Is There An Ongoing “Job”?

This factor can sound technical, but the idea is simple:

• Are you obliged to provide ongoing work?
• Is the contractor obliged to accept ongoing work?

A contractor engagement that’s genuinely project-based, with clear start and end points, tends to look less like employment than an open-ended arrangement where the contractor is treated like a permanent role.

4) Financial Risk And “In Business On Their Own Account”

Contractors typically carry some commercial risk. For example:

• They quote for a project and may need to fix defects at their own cost.
• They provide their own tools/software/equipment (depending on the industry).
• They can make a profit or loss on the engagement.
• They market their services to other clients.

If someone is paid like an employee (regular salary-like payments, no meaningful risk, integrated into benefits), it becomes harder to argue the arrangement is genuinely “outside IR35”.

5) Integration: Are They Part Of Your Business?

Ask yourself:

• Does the contractor appear on internal org charts?
• Do they manage your staff as if they’re a line manager?
• Do they have a company email signature that makes them look like an employee?
• Are they included in staff perks, appraisals, or “employee-only” processes?

None of these on their own is decisive, but the more “embedded” the person is, the more likely the relationship looks employment-like.

If you want your engagement to remain a true independent service relationship, it helps to structure it as such - including using the right type of contract, such as a properly drafted Contractor agreement or Consulting agreement, rather than relying on a generic template.

What Should Your Business Do To Comply With IR35? (A Practical Checklist)

Understanding IR35 is one thing. Running your business day-to-day is another.

Here’s a practical checklist to help you manage IR35 risk in a way that’s realistic for small businesses.

Step 1: Map Your Contractor Engagements

Start by getting visibility. List:

• Who you currently engage (and who you plan to engage)
• How they’re paid and who invoices whom
• Whether they operate through a PSC, as a sole trader, via an agency, or another structure
• What work they do and how integrated they are into your business

This helps you identify which relationships are higher risk and need a closer look.

Step 2: Carry Out A Status Assessment Before Work Starts

Ideally, you consider IR35 status at the start - not after someone has been working with you for 18 months.

When doing your assessment, focus on:

• what the contract says,
• what the working practices will be, and
• whether you can actually run the engagement that way in reality.

If you’re unsure, getting tailored advice early can be far cheaper than trying to fix issues later.

Step 3: Align The Contract With Reality

A strong contract is your foundation - but only if it matches how the work will actually happen.

For example, it’s no use having a “substitution” clause if your project manager tells the contractor “we only want you and no one else can do the work”. That inconsistency is exactly what creates risk.

Depending on the nature of the engagement, you might use a Freelancer agreement for more creative or project-based services, or a contractor agreement for ongoing specialist services.

Step 4: Set Boundaries In Day-To-Day Working Practices

This is the part many businesses miss. You can have a great contract, but if you manage a contractor like an employee, you may drift “inside IR35” over time.

Practical ways to reduce risk include:

• Define deliverables and milestones instead of controlling hours and attendance (where possible).
• Avoid giving contractors staff benefits or staff-only perks.
• Use project briefs and statements of work so the engagement stays outcome-focused.
• Avoid making contractors responsible for internal people management unless that’s part of an independent consultancy deliverable.

Step 5: Watch Out For “Long-Term Contractor” Arrangements

It’s common for a contractor to stay with a growing business for a long time. That doesn’t automatically create an IR35 issue, but it does increase the chance that:

• the contractor becomes embedded in your team,
• working practices drift into employee-like patterns, or
• the original scope becomes unclear and open-ended.

A good habit is to review contractor engagements periodically (for example, at renewal points) and update scopes and contracts where needed. If you’re changing the nature of a relationship, document it properly - sometimes with a formal Contract amendment.

What Legal Documents And Policies Help Reduce IR35 Risk?

IR35 is primarily a tax issue, but the way you document and run contractor arrangements can either protect you or expose you.

Here are the legal documents and supporting policies that often matter when you’re engaging contractors.

A Proper Contractor/Consultancy Agreement

Your agreement should clearly cover:

• Scope: what services are being delivered (and what isn’t included)
• Deliverables: outcomes, milestones, acceptance criteria
• Payment terms: fees, invoicing, expenses, late payment
• Control and independence: clarifying the contractor’s autonomy where appropriate
• Substitution: if relevant and genuinely workable
• IP ownership: who owns what is created during the engagement
• Confidentiality: protecting your sensitive information
• Termination: ending the engagement cleanly

This is also where you can avoid confusion between genuine contractor work and employment-like work. If the arrangement is closer to “part of the team”, you may be better off using an Employment Contract instead - and that decision is often better made early.

Clear IP And Confidentiality Protections

Many businesses bring on contractors for valuable work like software development, marketing assets, operational systems, or client delivery.

Don’t leave ownership unclear. If a contractor creates key assets for your business, you’ll want properly drafted IP and confidentiality clauses so you’re not left arguing later about who owns what, or what the contractor can reuse with another client.

Data Protection Terms (If Contractors Handle Personal Data)

If your contractor will have access to customer data, employee data, or any personal data, you should think about data protection up front.

In many cases, you’ll need appropriate terms covering privacy and security, and sometimes a Data processing agreement to make sure responsibilities are clear and you’re aligned with UK GDPR requirements.

This won’t “solve IR35” - but it will reduce the broader legal risk that often comes with engaging external providers.

Policies That Support Consistent Working Practices

As your team grows, IR35 risk often comes from inconsistency: one manager treats contractors like independent providers, another treats them like employees.

Consider documenting internal guidance on how contractors should be engaged and managed, especially around:

• who can approve contractor engagements,
• how scopes and deliverables are set, and
• what tools, access, and supervision are appropriate.

Even simple process controls can help you stay consistent and avoid accidental “inside IR35” working patterns.

Key Takeaways

• IR35 explained: IR35 targets “disguised employment”, where someone works like an employee but is engaged as a contractor through an intermediary.
• For small businesses, the biggest IR35 risk is often unexpected tax liability if HMRC later decides an engagement should have been treated as employment for tax purposes.
• Under the off-payroll rules, whether the engager must make a formal status decision can depend on whether the engager is “small” (broadly, meeting at least two of: turnover ≤ £10.2m, balance sheet total ≤ £5.1m, employees ≤ 50).
• If the off-payroll rules apply, the client must issue a Status Determination Statement (SDS) and take reasonable care when deciding whether the engagement is inside or outside IR35.
• Liability can depend on the supply chain: typically, the fee-payer is responsible for PAYE/NIC deductions where the off-payroll rules apply, but liability can shift (for example, if the SDS is not properly issued or where parties in the chain fail to meet their obligations).
• IR35 status depends on real working practices, especially control, substitution, and whether the engagement looks like an ongoing job rather than a project.
• A solid contract helps, but your day-to-day practices must match what the contract says - otherwise you’re exposed.
• Use the right documentation (like a contractor or consulting agreement) and review long-term engagements so the relationship doesn’t drift into employee-like arrangements.
• If contractors handle personal data, make sure you have appropriate privacy and security terms in place, which may include a data processing agreement.

Important: This article is general information and isn’t tax advice or an IR35 status determination. IR35 outcomes are highly fact-specific, and you should consider speaking with a qualified tax adviser or accountant for an IR35 assessment.

If you’d like help putting the right legal paperwork in place for a contractor engagement (and aligning contracts with how you actually work), you can reach us at 08081347754 or team@sprintlaw.co.uk.