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IR35 Explained for International Employers Hiring in the UK
If you are hiring contractors in the United Kingdom, IR35 is not something you can afford to ignore. The UK's off-payroll working rules have been around since April 2000, and they were significantly tightened in April 2021 for medium and large organisations. The rules determine whether a contractor is genuinely self-employed or, for tax purposes, should be treated as an employee. Get it wrong and the financial penalties are severe: unlimited fines and, in the worst cases, criminal charges.
This guide breaks down what IR35 actually means, how the rules work in practice, and why international employers need to pay close attention. Whether you are setting up a UK team for the first time or already engaging contractors here, understanding IR35 is essential for staying compliant with HMRC regulations.
Need support managing UK contractor compliance? Agility EOR handles IR35 assessments as part of our Employer of Record service.
What Exactly Is IR35 and Why Does It Exist?
IR35 refers to a set of UK tax rules officially known as the "off-payroll working rules." The name comes from the original press release number issued by HMRC (Her Majesty's Revenue and Customs) when the rules were first announced. The legislation itself is found in the Income Tax (Earnings and Pensions) Act 2003 (ITEPA 2003), specifically Chapter 10 of Part 2.
The purpose of IR35 is straightforward. It exists to prevent what HMRC calls "disguised employment." This is where a person works like an employee but operates through an intermediary, usually a personal service company (PSC), to pay less tax and National Insurance. Without IR35, it would be simple for someone to leave their job on a Friday, set up a limited company on Monday, and do the exact same work while paying significantly less tax.
The rules apply when a contractor provides services through an intermediary. If the working relationship looks and feels like employment, IR35 says the contractor should be taxed as an employee, regardless of the paperwork or company structure.
For international employers, this is particularly important. If you are engaging UK-based contractors from abroad, the rules still apply to you. Ignorance of UK tax law is no defence, and HMRC has become increasingly aggressive in pursuing non-compliant arrangements.
How Has IR35 Changed Since It Was Introduced?
The story of IR35 is one of gradual tightening over more than two decades.
When IR35 was first introduced in April 2000, the responsibility for determining employment status sat squarely with the contractor. The contractor decided whether they were inside or outside IR35 and paid the appropriate taxes. In practice, this led to widespread non-compliance. Many contractors simply declared themselves outside IR35 without any real assessment, and HMRC lacked the resources to challenge them.
For 21 years, this system limped along. HMRC lost high-profile cases against presenters at the BBC and other media organisations, which exposed the weaknesses of the original framework.
Then came the April 2021 reforms, which fundamentally changed who decides. In the public sector (which had changed in 2017), and now in the private sector for medium and large companies, the responsibility shifted. It is now the end client that must determine whether a contractor is inside or outside IR35. If the client gets it wrong, the liability for unpaid tax and National Insurance shifts to them.
This was a seismic change. Suddenly, the organisation hiring the contractor bore the financial risk of misclassification. The reforms also introduced the requirement for a Status Determination Statement (SDS), which must be passed down the supply chain.
Want to understand how IR35 fits into broader UK employment compliance? Our guide on UK employment law covers the full landscape.
Who Does IR35 Apply To?
IR35 applies in two main scenarios, depending on the size of the end client.
For medium and large private companies and all public sector bodies: The end client is responsible for determining the contractor's IR35 status. They must issue a Status Determination Statement and, if the contractor is deemed inside IR35, ensure the correct tax and NICs are deducted.
For small private companies: The original rules still apply. The contractor's own PSC remains responsible for determining their status and paying the appropriate taxes. A company is considered "small" if it meets two of three criteria: turnover of £15 million or less, a balance sheet total of £7.5 million or less, or 50 employees or fewer. (These limits were raised from £10.2 million and £5.1 million for financial years starting on or after 6 April 2025; HMRC says this won't change off-payroll status until 6 April 2027 at the earliest.)
For international employers, the critical question is where your company falls. If you are a medium or large business, you are responsible for assessing every UK contractor you engage. The location of your headquarters does not matter; what matters is where the work is performed and the size of the engaging organisation.
Here is a practical example
A US-based software company with 200 employees engages a UK contractor through the contractor's PSC to build a new feature. The US company is a medium/large organisation by UK standards, so it must assess the contractor's IR35 status. If it fails to do so and the contractor is later found to be inside IR35, the US company is liable for the unpaid tax.
If replacing the contractor relationship with employment feels complex, read our comparison of EOR vs Umbrella to understand your options.
How Do You Determine a Contractor's IR35 Status?
Determining whether a contractor falls inside or outside IR35 is not a tick-box exercise. It requires an assessment of the actual working relationship, not just the contract. HMRC and, if it comes to it, tax tribunals will look at what happens in practice.
The key factors are:
Does the client control what work is done, when it is done, where it is done, and how it is done? The more control the client exercises, the more the arrangement looks like employment. A genuine contractor should have autonomy over how they deliver the work.
Could the contractor send someone else in their place to do the work? A genuine right of substitution is a strong indicator of self-employment. If the contractor must do the work personally, it points towards employment.
Is there an ongoing obligation for the client to provide work and for the contractor to accept it? If so, this suggests employment. A true contractor engagement is project-based with no expectation of continued work.
Does the contractor bear any financial risk? For example, do they invoice for work, have to fix errors at their own cost, or provide their own equipment? Financial risk is a hallmark of genuine self-employment.
Is the contractor integrated into the client's organisation? Do they have a company email, attend staff meetings, manage employees, or receive employee benefits? The more integrated they are, the more they look like an employee.
The HMRC CEST Tool
HMRC provides the Check Employment Status for Tax (CEST) tool, which is an online questionnaire that gives a determination based on the answers provided. You can find it on GOV.UK.
The CEST tool is a reasonable starting point, but it has limitations. It has been criticised for producing "undetermined" results in borderline cases, and some tribunal decisions have contradicted CEST outcomes. HMRC has said it will stand by CEST results if the questions are answered accurately, but many employment law specialists recommend using CEST alongside professional advice.
If you are an international employer with limited knowledge of UK employment law, relying solely on CEST is risky. A proper assessment, ideally documented and reviewed by a specialist, is the safer approach.
For a broader view on engaging UK workers compliantly, see our article on UK contractor to employee.
What Happens If You Get IR35 Wrong?
The penalties for IR35 non-compliance are among the most severe in UK employment tax.
If HMRC determines that a contractor should have been treated as inside IR35, the following liabilities arise:
The deemed employer must pay the income tax and employee National Insurance contributions that should have been deducted. This is calculated on the full value of fees paid to the contractor's PSC.
The deemed employer must also pay the employer's National Insurance contributions on top.
HMRC will charge interest on the unpaid tax from the date it should have been paid. Penalties for careless errors range from 0% to 30% of the unpaid tax. For deliberate errors, penalties can reach 100%. For deliberate and concealed errors, they can go up to 200%.
In extreme cases involving deliberate tax evasion, HMRC can pursue criminal charges. While this is rare for IR35 cases, it is possible, particularly where there is evidence of fraudulent intent.
HMRC can go back up to six years to investigate, or up to 20 years in cases of deliberate non-compliance. For a company that has been engaging contractors for years without proper assessments, the backdated liability can be enormous.
A real-world example illustrates the risk. In 2022, HMRC pursued several large organisations for IR35 failures dating back years. The liabilities, including tax, NICs, interest, and penalties, ran into millions of pounds. These were not obscure companies; they were well-known names that should have known better.
Understanding the full picture of UK employment law helps you avoid these pitfalls. Explore our EOR vs entity guide to understand the different ways you can engage UK workers.
What Does IR35 Mean for International Employers Specifically?
If you are an international employer with no UK entity, IR35 creates a specific set of challenges.
First, you are still in scope. HMRC does not care where your company is incorporated. If you are engaging UK-based individuals to do work in the UK, the off-payroll working rules apply. You still need to assess status, issue the SDS if you are a medium or large business, and ensure the correct tax is paid.
Second, you may not have the infrastructure to do this properly. You might not have a UK payroll, a UK bank account, or a UK-based HR team. This makes compliance harder but no less important.
Third, if you get it wrong, HMRC will pursue you for the unpaid tax. Collecting from an overseas company is more difficult for HMRC, but it is by no means impossible. HMRC has international collection agreements with many countries, and it can also take action against your UK-based contractors or any UK assets.
Fourth, the reputational risk is real. If you are known in your industry as a company that does not comply with UK tax rules, it will be harder to attract the best UK talent, whether as contractors or employees.
How Does an Employer of Record Handle IR35?
This is where an Employer of Record, or EOR, becomes a genuinely valuable solution for international employers.
An EOR based in the UK, such as Agility EOR, takes on the legal responsibility for employing your UK workers. Instead of engaging contractors through PSCs and navigating IR35 yourself, the EOR employs the workers directly on your behalf.
Here is how it works in practice. You identify the talent you want to bring on. Instead of asking them to invoice you through their PSC, the EOR hires them as employees. The workers carry out your day-to-day direction and project work, but their legal employer is the EOR.
This approach sidesteps IR35 entirely. Because the workers are employees of the EOR, there is no intermediary in the IR35 sense. The off-payroll working rules simply do not apply. The EOR handles all tax deductions, National Insurance contributions, pension auto-enrolment, and compliance with UK employment law.
For you as the international employer, this means:
There is no assessment to get wrong because there is no contractor arrangement.
The EOR operates a PAYE (Pay As You Earn) payroll, deducting the correct tax and NICs at source.
You do not need to issue SDS statements, run a UK payroll, or deal with HMRC.
Your team members get the security of employment, including statutory rights like sick pay, holiday pay, and pension contributions.
The EOR model is not a loophole. It is a legitimate, well-established approach used by thousands of international companies to hire UK talent compliantly. In fact, it is often the simplest and most cost-effective option for companies that want to build a UK team without the expense and complexity of setting up a UK entity.
For international employers navigating UK employment law, Agility EOR provides a complete solution. Our UK EOR service handles IR35, payroll, employment contracts, and all statutory obligations on your behalf.
Agility EOR is far more than just a service provider. We’re flexible, innovative and focused on outstanding client service. Supporting you every step of the way – and valuing your people as the cornerstone of success.
Frequently Asked Questions
Yes. If you are engaging individuals who work in the UK, the off-payroll working rules apply regardless of where your company is based. The determining factors are where the work is performed and the size of your organisation, not the location of your headquarters.
If a contractor is inside IR35, they are deemed to be an employee for tax purposes. Income tax and NICs must be deducted at source, and the engaging company must pay employer NICs. If a contractor is outside IR35, they are genuinely self-employed and can pay themselves through their PSC in a tax-efficient manner.
Yes, the CEST tool is freely available on GOV.UK and can be used by any organisation. However, it is designed around UK employment law concepts, and its results should be interpreted by someone with knowledge of the UK framework. Using CEST alone, without professional advice, is not recommended for international employers.
An SDS is a formal document that the end client must produce after assessing a contractor's IR35 status. It records the determination (inside or outside IR35) and the reasons for it. The SDS must be shared with the contractor and passed down the labour supply chain.
HMRC can investigate up to six years back for innocent errors. For careless errors, the period is also six years. For deliberate non-compliance, HMRC can go back up to 20 years. In the most serious cases involving fraud, there is no time limit.
Speak to an expert
If you are hiring in the UK and want to eliminate IR35 risk entirely, Agility EOR can help. We employ your UK team members directly, handle all payroll and tax compliance, and ensure every statutory obligation is met. Find out how our UK Employer of Record service works.