IR35 for Trade Contractors UK — What Self-Employed Tradespeople Need to Know (2026)

IR35 — formally known as the off-payroll working rules — is a piece of tax legislation that catches people working as "disguised employees" through a limited company. For trade contractors operating through a personal service company (PSC), it's one of the most important compliance issues to understand. Get it wrong and HMRC can reach back six years, recovering unpaid Income Tax and National Insurance with penalties on top.

This guide explains what IR35 is, who it affects in the trades, how the three-part employment status test works, how CIS and IR35 interact, and what steps you can take to protect an outside IR35 status — or manage your position if you're inside.

What is IR35?

IR35 was introduced in April 2000 by the then-Inland Revenue (now HMRC) to tackle a specific tax avoidance pattern. Individual workers were leaving employment, setting up personal service companies, then returning to do the same job for the same client — paying Corporation Tax and dividends rather than the higher Income Tax and National Insurance liabilities of an employee.

The rules were significantly reformed in 2017 (for public sector engagements) and again in April 2021 (for medium and large private sector clients). These "off-payroll working rules" shifted responsibility for determining IR35 status from the contractor to the end client in many cases.

If HMRC determines you should be inside IR35 for a given engagement, you are treated as an employee of your client for tax purposes. Your limited company income from that engagement is taxed as employment income: you pay Income Tax at your marginal rate and Class 1 National Insurance, with no dividend tax advantages. You do not receive employment rights such as paid holiday or sick pay — the worst of both worlds.

Who does IR35 affect in the trades?

IR35 is only relevant if you operate through a limited company (or other intermediary such as a partnership where the worker holds more than 60% of the interest). If you are a sole trader — whether under CIS or general self-assessment — IR35 does not apply to you. Your employment status is determined separately through the normal employed vs self-employed tests, but IR35 as a specific set of rules only targets intermediary structures.

In the construction and trades sector, the contractors most exposed to IR35 are:

• Trade contractors billing a main contractor or developer through their own limited company — for example, an electrician running “ABC Electrical Ltd” and invoicing a main contractor for labour on a housing development.
• Specialist subcontractors on long-term project placements — working on a single site for months at a time under direct supervision of the main contractor's site management team.
• Labour-only subcontractors (LOSC) operating through a limited company — where all materials and equipment are supplied by the main contractor and only labour is being provided.

IR35 is not the same as CIS. The Construction Industry Scheme is a tax withholding mechanism that applies to construction work regardless of business structure. CIS and IR35 are separate regimes — more on this below.

The three key IR35 factors

HMRC assesses IR35 status by looking at the actual working arrangement — not just what is written in the contract. Three factors carry the most weight:

1. Substitution

Can you send another suitably qualified person to do the work in your place, without the client having the right to reject them? A genuine right of substitution — where the client must accept a substitute, not just a specific individual — is one of the strongest indicators of self-employment.

In the trades, this needs to be realistic. A Gas Safe registered engineer cannot substitute with an unqualified worker — but they could substitute with another Gas Safe registered engineer. HMRC accepts that qualification-constrained substitution is still genuine substitution, provided the clause in the contract reflects this and there is genuine practical ability to substitute.

If your contract (or working practice) requires you personally to turn up — and the client would refuse a substitute — this points toward an inside IR35 determination.

2. Control

Who decides how, where and when the work is done? In genuine self-employment, the contractor determines the method and sequence of work, uses their own equipment and expertise, and delivers an agreed outcome. The client specifies what they want — not how to do it.

In the trades, working on a large construction site will always involve some degree of co-ordination — start times, sequencing with other trades, health and safety compliance. HMRC distinguishes between reasonable site management (acceptable) and day-to-day direction of the way you carry out your trade (indicative of employment). A site manager telling you which floor to work on is different from a site manager telling you how to install a consumer unit.

Red flags include: being given company email addresses or uniforms, being required to attend company meetings, being managed on performance metrics, or being told how to carry out specific technical tasks.

3. Mutuality of obligation

Mutuality of obligation (MOO) asks whether there is an implied or explicit obligation on the client to offer you work and on you to accept it. In an employment relationship, both exist: the employer keeps providing work, the employee keeps turning up. In genuine self-employment, the contractor can walk away and the client can use someone else.

For trade contractors, working exclusively for one main contractor for an extended period — especially if there is an expectation on both sides that the relationship will continue — raises MOO concerns. Working for multiple clients concurrently, or on a clearly defined project with a fixed end date and no expectation of follow-on work, reduces the risk.

The off-payroll working rules post-2021

Since April 2021, the off-payroll working rules have changed who bears responsibility for determining IR35 status in the private sector:

• Medium and large private sector end clients are responsible for assessing the IR35 status of contractors they engage. They must issue a Status Determination Statement (SDS) — a written document explaining their status decision and the reasons for it — before or on the date they start using the contractor.
• The fee-payer — usually the agency or main contractor sitting between the end client and your limited company — is responsible for operating PAYE if the engagement is determined to be inside IR35. They deduct Income Tax and National Insurance from your invoice before paying you.
• Small end clients are exempt from these rules. A small company is one that meets at least two of: annual turnover no more than £10.2m, balance sheet total no more than £5.1m, no more than 50 employees. If your end client is a small company, you (your limited company) are still responsible for determining your own IR35 status — the old regime applies.

You have the right to challenge a Status Determination Statement if you believe it is wrong. The end client must have a formal disagreement process and must respond within 45 days. If the client fails to respond, liability for any underpaid tax transfers back to them.

IR35 vs CIS — the key distinction

These two regimes are frequently confused, including by contractors themselves. Here is the key difference:

• CIS (Construction Industry Scheme) is a tax withholding mechanism that applies to payments for construction work in the UK. It covers sole traders, partnerships, limited companies and individuals working in construction. When a main contractor pays a CIS subcontractor, they deduct 20% (or 30% for unregistered subcontractors) at source and pay it to HMRC. CIS is not an employment status test — it says nothing about whether you are an employee or self-employed.
• IR35 is an employment status test specifically for workers operating through a limited company or other intermediary. It asks: should this person be taxed as an employee? It only applies if there is a limited company in the payment chain.

You can be subject to CIS and also need to consider IR35. A limited company carrying out construction work receives payments net of CIS deductions. If that engagement is also inside IR35, the fee-payer must additionally operate PAYE on the labour element of the invoice — meaning both CIS and PAYE treatment may apply, which creates a complex overlap that an accountant familiar with construction tax needs to handle.

For sole traders under CIS, IR35 is simply not relevant. You are already assessed as self-employed or employed through standard employment status tests, and CIS handles the advance deduction of your Income Tax.

Signs your engagement might be inside IR35

Not every trade contractor engagement is high risk, but the following factors individually or in combination increase the likelihood of an inside determination:

• You work for a single main contractor for long continuous periods with no breaks.
• You follow the main contractor's site hours and are directed on a daily basis by their management team.
• The contract has no meaningful substitution clause — or you have never exercised any right to substitute.
• All materials, PPE and equipment are supplied by the client — you are providing labour only.
• You have no financial risk: you are paid a day or week rate regardless of whether the job overruns or goes wrong.
• You are integrated into the client's business — using their systems, attending their team meetings, wearing their branded workwear.
• Both you and the client expect the arrangement to continue indefinitely.

Protecting an outside IR35 status

If your working practices genuinely reflect self-employment, you can take practical steps to ensure the documentary and contractual evidence supports that position:

• Have a proper written contract for each engagement that includes a genuine substitution clause, does not require you personally, and specifies the output (the work to be done) rather than your time.
• Use your own tools and equipment. A tradesperson using their own van, power tools and PPE looks more self-employed than one who uses everything supplied by the client.
• Work for multiple clients. Multiple concurrent clients is strong evidence against mutuality of obligation with any single client.
• Control your working methods. Make decisions about how the technical work is done without being directed by the client's staff.
• Carry your own professional insurance — public liability and professional indemnity in your company name demonstrate you are running a business at financial risk.
• Take on financial risk. Fixed-price contracts, where you bear the cost of running over, demonstrate the risk/reward dynamic of genuine self-employment rather than employment.
• Keep records of each engagement — contracts, CEST results, correspondence with clients about status determinations.

HMRC's CEST tool

HMRC provides the Check Employment Status for Tax (CEST) tool free on GOV.UK. It takes you through a structured set of questions about your working arrangement and returns one of three outcomes: employed, self-employed, or unable to determine.

CEST is not a perfect tool — it has been criticised for how it handles mutuality of obligation — but HMRC has committed to stand by CEST results where the facts entered are accurate and complete. This means:

• Run CEST before each new engagement, or when your working arrangements change significantly.
• Answer every question honestly based on the actual working practices, not the ideal scenario.
• Save a PDF or screenshot of the result and store it with your engagement documentation.
• If CEST returns "unable to determine," seek professional advice — your situation is genuinely borderline.

CEST is a starting point, not a guarantee. For higher-value or longer-term engagements, a contractor-specialist accountant or employment status barrister can give you a more reliable assessment.

Consequences of getting it wrong

IR35 non-compliance is not a minor administrative matter. If HMRC investigates and determines that an engagement was inside IR35:

• HMRC can recover unpaid Income Tax and National Insurance going back up to six years (or longer in cases of deliberate non-compliance).
• Interest on the unpaid tax accrues from the original due date.
• Penalties apply — up to 30% of unpaid tax for careless errors, up to 100% for deliberate concealment.
• Medium and large end clients who fail to carry out status determinations correctly, or fail to issue an SDS, become liable for the tax themselves — a significant financial risk for main contractors engaging labour-only subcontractors through limited companies.

It is worth being clear on one thing: HMRC does investigate the construction sector specifically. The use of limited companies by labour-only subcontractors is a known compliance focus area. If your engagement looks like employment — long duration, single client, daily direction, no substitution — the risk of scrutiny is real.