UK Construction: Subcontractor IR35 Compliance (Avoid £50K+ Penalties)
- The Construction IR35 Trap
- Risk Factors
- AskBiz IR35 Documentation
- CIS and IR35 Are Different Rules — And Both Apply in Construction
- A Groundworks Firm's HMRC Status Check on a Housing Development
- What CEST Can and Cannot Tell a Construction Business
- Documenting a Proper Status Determination Statement
- How Ordinary Job Records Build the Independence Paper Trail
Construction subcontractor works on client job-site 5 days/week, using client's tools, following client's instructions. Looks like employee. HMRC audits, determines "caught red-handed." Back-tax: 30-40% of 3 years income = £30K-50K+. AskBiz documents genuine independence (multiple clients, own tools, take business risk).
- The Construction IR35 Trap
- Risk Factors
- AskBiz IR35 Documentation
- CIS and IR35 Are Different Rules — And Both Apply in Construction
- A Groundworks Firm's HMRC Status Check on a Housing Development
The Construction IR35 Trap#
Construction industry has high IR35 failure rate. Subcontractors work on-site, look like employees. HMRC challenge often succeeds. Typical outcome: £40K-80K back-tax bill.
Risk Factors#
(1) One client (high risk). (2) Supplied tools (vs. own tools). (3) Work on client-site. (4) Set hours. (5) Integrated into team. All point to employment, not self-employment.
AskBiz IR35 Documentation#
Proves independence: (1) Multiple projects/clients. (2) Own tools and equipment. (3) Can choose how/when to work. (4) Take financial risk (if project fails, you lose money). (5) Charge own rates. Strong documentation defends against HMRC audit.
CIS and IR35 Are Different Rules — And Both Apply in Construction#
Construction is one of the few sectors where two entirely separate sets of tax rules apply simultaneously to the same subcontractor relationship, and confusing the two is one of the most common mistakes contractors and subcontractors make. The Construction Industry Scheme governs how payments are made from a contractor to a subcontractor — under CIS, the contractor deducts money at source from payments to most subcontractors and passes it to HMRC as an advance towards the subcontractor's tax and National Insurance, with the deduction rate depending on whether the subcontractor is registered with HMRC and verified. This is fundamentally a payment and withholding mechanism, and being processed through CIS says nothing on its own about whether the subcontractor is genuinely self-employed or should, for tax purposes, be treated as an employee. That second question — genuine self-employment status — is exactly what IR35 and the off-payroll working rules address, looking at the actual working relationship: control, substitution, mutuality of obligation, and financial risk, regardless of how payments are processed. A subcontractor can be correctly registered and deducted under CIS while simultaneously failing an IR35 status test because, in practice, they work like an employee — same client, fixed site hours, told exactly what to do and how, using tools and materials the contractor supplies. Equally, a subcontractor can be outside CIS deduction entirely for certain types of work and still have their status scrutinised under IR35 principles if they operate through a limited company. Treating CIS registration as proof of self-employed status is a common and costly assumption — it proves nothing about status, only about how the money moved.
A Groundworks Firm's HMRC Status Check on a Housing Development#
A groundworks subcontracting firm, working through a limited company with two directors and no other employees, had spent the better part of a year working almost exclusively on a single large housing development for one main contractor, arriving on site at the same time each morning as the contractor's own directly employed groundworkers, using welfare facilities and some plant equipment supplied by the main contractor, and taking instructions each day from the same site manager who also directed the contractor's own staff. When HMRC opened a status review — triggered, as these often are, by a broader compliance check into the main contractor's subcontractor arrangements across several sites rather than anything specific to this one firm — the groundworks company found itself needing to demonstrate genuine independence for a working pattern that, described plainly, looked very close to employment. The firm did have some points in its favour: it owned its own excavator and smaller plant, it had worked for two other contractors earlier in the same tax year before this development absorbed all its capacity, and it invoiced for completed phases of work rather than being paid an hourly or daily rate. But the sustained single-client relationship, the shared site facilities, and the day-to-day direction from the main contractor's site manager were the kind of factors that make a status determination genuinely contestable rather than clear-cut in either direction. The review process took months, required the firm to reconstruct records of other client work, plant ownership, and invoicing patterns going back over a year, and created a period of real uncertainty for both the subcontractor and the main contractor over who would be liable for any additional tax if the determination went against self-employed status.
What CEST Can and Cannot Tell a Construction Business#
HMRC provides an online tool, generally known by its short name CEST, intended to help contractors and subcontractors work through the status factors and reach a determination. It asks a structured series of questions about control, substitution, and the working arrangement, and produces an output indicating whether the engagement looks like it falls inside or outside the off-payroll rules. For straightforward cases, it can be a genuinely useful starting point and a way to document that a reasonable, structured assessment was carried out at the time. Its practical limitations in construction, however, are worth understanding rather than treating the tool's output as a final word. Construction working patterns are often genuinely mixed and site-specific in ways that a general-purpose questionnaire can struggle to capture precisely — the degree of on-site direction can vary week to week depending on the phase of work, a subcontractor might be substitutable in principle but has in practice never actually sent a substitute, and site safety requirements that apply to everyone on site regardless of employment status can look, to an automated tool, like the kind of control that suggests employment even where it is really just standard site management. Because of this, most sensible practice in the sector treats a tool-generated result as one input into a status determination rather than the determination itself — it should be paired with a genuine, honest look at the real day-to-day relationship, ideally documented in enough detail that if HMRC ever asks how the determination was reached, there is a clear paper trail beyond a single tool output.
Documenting a Proper Status Determination Statement#
Under the off-payroll working rules, where they apply, the party responsible for determining status must produce a status determination statement setting out the conclusion reached and the reasoning behind it, and pass that statement to the subcontractor and to the party they are contracting with. Doing this properly is a practical discipline, not just a compliance box-tick. It starts with gathering the real facts of the engagement before writing anything down: how many other clients has the subcontractor worked for in the relevant period, who supplies the main tools and plant used, who sets the working hours and who directs the day-to-day work, whether the subcontractor has ever sent a substitute or could genuinely do so, and what financial risk the subcontractor carries — do they invoice for completed work regardless of hours spent, do they correct defects at their own cost, do they quote fixed prices that could result in a loss if a job overruns. The determination statement should then set out the conclusion against each of these factors specifically, rather than a generic one-line assertion of self-employed status, because a specific, factor-by-factor determination is far more defensible if challenged than a blanket statement. This should be revisited whenever the working pattern changes materially — a subcontractor who starts a project working across several sites for several clients but ends up, months later, effectively embedded full-time on one site for one contractor has had their status circumstances change, and the determination should be revisited to reflect that rather than left as a stale document from the start of the relationship.
How Ordinary Job Records Build the Independence Paper Trail#
The strongest evidence of genuine self-employment in an HMRC status review is rarely a single document written specifically to argue the case — it is the accumulated, ordinary record of how a subcontracting business actually operates, recorded consistently over time as a normal part of running the business rather than assembled defensively after a review has already started. A subcontractor who invoices multiple concurrent or sequential clients, purchases their own materials and plant against their own accounts, and works to genuinely varied site schedules rather than a single fixed daily routine builds exactly this kind of record simply by operating normally and keeping proper accounts. AskBiz's job and invoice tracking captures this naturally: separate jobs logged against separate clients show client diversity over time rather than a single relationship dressed up as several; materials and equipment purchases recorded against specific jobs demonstrate the subcontractor is bearing genuine costs and financial risk rather than simply turning up and being supplied everything; and job-level scheduling data shows working patterns varying by site and by client rather than a fixed, employee-like routine repeated week after week. None of this is created specifically for an IR35 defence — it is simply what proper job costing and invoicing looks like for a well-run subcontracting business — but when a status review does happen, having months or years of this data ready to export and present is a materially stronger position than trying to reconstruct it from memory and paper invoices under time pressure, which is exactly the scramble the groundworks firm on the housing development found itself in.
People also ask
How do I stay IR35-compliant in construction?
Multiple clients, own tools, control work methods, take business risk. Avoid: single client, client-supplied tools, fixed hours.
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