What a deemed contractor is
Under the Construction Industry Scheme, the word "contractor" covers more than construction businesses. Any organisation that spends enough on construction work is brought into the scheme as a deemed contractor, regardless of what its actual trade is.
The test is straightforward. If a business's construction expenditure reaches £3 million within a rolling 12-month period, it becomes a deemed contractor and must register for CIS, verify subcontractors, make deductions and file monthly returns, in exactly the same way as a plumbing company or groundworks firm. The label on the business is irrelevant. The spending threshold is the trigger.
This rule exists because large non-construction organisations routinely commission substantial construction work, refitting buildings, expanding campuses, building new facilities, and leaving them outside the scheme would create a significant gap in HMRC's ability to collect tax from the subcontractors doing the work. Parliament's solution was to treat them as contractors once their spend passes the threshold.
Who the threshold catches
The £3 million threshold sounds specific, but the range of organisations it draws in is wide. Any entity running a sustained capital programme or large-scale building maintenance budget can find itself inside CIS. The most common examples include:
- Retail chains commissioning multiple store refits or fitting out new sites.
- Housing associations refurbishing social housing stock.
- NHS trusts building wards, diagnostic centres or upgrading hospital infrastructure.
- Local authorities building schools, roads and public amenities.
- Universities expanding campuses or maintaining estate.
- Hotel groups undertaking major property refurbishments.
- Large facilities management businesses that subcontract construction and maintenance work on behalf of clients.
None of these organisations think of themselves as construction businesses. That is precisely the misunderstanding that lands them in difficulty. The test is not "are you in construction?" but "has your construction spend reached £3 million across the last 12 months?"
How the rolling 12-month test works in practice
Because the test runs on a rolling 12-month window, a single large capital project can pull an organisation over the threshold even if its usual construction spend is modest. A university spending £1 million a year on estate maintenance that then commissions a £12 million building crosses the £3 million line within the 12-month window in which that project spend lands. It does not wait for any multi-year average to build up. The obligation to register arises immediately, before the next subcontractor payment, once the rolling 12-month total reaches £3 million.
Once registered, the business stays inside CIS until it can satisfy HMRC that it should no longer be treated as a contractor. Broadly, that requires construction spend to have fallen below £1 million in each of three successive years, or for the business to stop commissioning construction work. There is no automatic exit at the end of a project. The practical implication is that any organisation planning a large capital programme should model whether the spend crosses the threshold before subcontractors are engaged, not after. Registering under time pressure while managing a live construction programme is significantly harder.
Deemed contractor vs mainstream contractor: what is the same and what differs
Once the threshold is crossed, a deemed contractor's CIS obligations are identical to those of a contractor whose trade is construction. The only difference is the trigger. Everything that follows from registration is the same.
| Feature | Mainstream contractor | Deemed contractor |
|---|---|---|
| Who they are | A business whose trade is construction work | A business outside construction whose construction spend reaches £3m in a rolling 12-month period |
| Registration trigger | Before the first subcontractor payment | When construction spend reaches £3m within a rolling 12-month period |
| Typical businesses | Builders, groundworkers, electricians, plumbers, roofers | Retailers, housing associations, NHS trusts, hotels, universities, local authorities, large FM businesses |
| CIS verification duty | Yes, before every subcontractor payment | Yes, before every subcontractor payment |
| Deduction rates | 0% (GPS) / 20% (registered) / 30% (unregistered) | 0% (GPS) / 20% (registered) / 30% (unregistered) |
| Monthly CIS300 return | Yes, due by the 19th of the following tax month | Yes, due by the 19th of the following tax month |
| Nil return obligation (from April 2026) | Yes, mandatory in months with no payments | Yes, mandatory in months with no payments |
| April 2026 GPS due-diligence duty | Yes | Yes |
| Knowledge-based penalty (ss.62A/62B) | Yes: 20% of the payment / sums returned, on the payer or return-maker | Yes: 20% of the payment / sums returned, on the payer or return-maker |
The deduction applies to the labour element only. On a £10,000 invoice made up of £6,000 labour and £4,000 materials, the deduction is applied to £6,000: a registered subcontractor loses £1,200 (20%), an unregistered one loses £1,800 (30%), and a GPS holder loses nothing. Getting this right is a day-one obligation.
The full monthly obligation chain
For an organisation that has never run CIS, the monthly cycle is a new process to build from scratch. Tax months run to the 5th; the return covers the month just ended.
- Verify each subcontractor with HMRC before the first payment to confirm GPS (0%), registered (20%) or unregistered (30%). Verification is online via HMRC's CIS service or by phone on 0300 200 3210. Our guide to verifying subcontractors under CIS covers the mechanics.
- Calculate and apply the deduction to the labour element only. Record the gross payment, the materials element excluded from the base, the rate applied and the net paid.
- Issue a payment and deduction statement (PDS) to each subcontractor showing the gross amount, deduction and net received. Subcontractors need this to reclaim any overpayment at the year end.
- File the CIS300 return by the 19th of the following tax month. If no payments were made in the month, a nil return is still required from April 2026.
- Pay deducted amounts to HMRC by the 22nd (electronic) or the 19th (cheque). Deducted CIS is not the contractor's money; it must not be treated as working capital.
Our guide to CIS for contractors: monthly responsibilities covers the full cycle in sequence.
What changes from April 2026
Finance Act 2026 introduced three changes from 6 April 2026 that apply to all contractors, including deemed contractors. Our guide to the April 2026 CIS rule changes covers the full picture; the key points for deemed contractors are below.
Nil returns are mandatory again
The CIS300 nil-return obligation was removed in 2015 and reinstated from 6 April 2026. A deemed contractor with no construction payments in a given tax month must still file a nil return by the 19th, or pre-notify HMRC of inactivity. Penalties start at £100 for one day late, rising to £200 at two months, then £300 or 5% of the CIS deductions on the return (whichever is higher) at six months, and again £300 or 5% at twelve months, with a further penalty of up to £3,000 or 100% of the deductions where information is withheld deliberately. For a deemed contractor with seasonal or project-driven spend, quiet months are not an exemption from filing.
The GPS due-diligence duty and the "knew or should have known" standard
Finance Act 2026 introduces an immediate GPS revocation power where HMRC concludes a contractor knew or should have known about fraud in the supply chain. A failure to carry out due diligence is itself sufficient to meet that standard. The three steps that satisfy it: re-verify each subcontractor's CIS status with HMRC before payment; run a Companies House legitimacy check; and carry out bank account name verification. Deemed contractors need to build these checks into their payment approval process and be able to evidence them.
Knowledge-based penalties under sections 62A and 62B
New sections 62A and 62B of Finance Act 2004 (inserted by Finance Act 2026) charge a person who makes a payment, or a return, knowing that a connected party has deliberately failed to comply with CIS. The penalty is 20% of the payment (s.62A) or 20% of the sums the return treats as paid (s.62B), and it attaches to the payer or return-maker, which may be a company or an individual. Where a company's behaviour produces these penalties, HMRC can pursue its officers personally under the existing officer-liability rules. For the finance director or CEO of an organisation in deemed contractor status, the message is that CIS compliance is now a personal as well as a company-level matter, and the due-diligence steps above are the way to manage that exposure.
Common misconceptions
Two misunderstandings come up consistently when organisations first learn they may be deemed contractors.
The first is "we are not in construction, so CIS does not apply to us." As the section above explains, this is the wrong test. Being outside the construction trade is not an exemption. Construction spend reaching £3 million within a rolling 12-month period is the trigger, and the nature of the organisation's main business is irrelevant. An NHS trust, a supermarket chain or a university is as capable of being a deemed contractor as a house builder.
The second is "the project finished, so we are out." CIS registration does not end when a project ends. A deemed contractor remains in the scheme until it can satisfy HMRC that it should no longer be treated as a contractor, broadly once construction spend has been below £1 million in each of three successive years (or it stops commissioning construction work). An organisation that ran a £15 million programme will stay inside CIS well after the building is finished, even if it commissions nothing further, until that exit condition is met.
Practical steps for a business approaching the threshold
If your organisation's construction spend is approaching £3 million a year, act before the threshold is crossed.
- Track the rolling 12-month total. Add up actual construction spend across the most recent 12 months and project it forward as new commitments are made. If the running total is approaching £3 million, the obligation may be about to arise, or may already have done so.
- Appoint a CIS specialist. Penalties for errors accumulate quickly, and the April 2026 changes have raised the compliance bar. Specialist support before registration costs far less than correcting errors after the fact.
- Set up a verification process. Every subcontractor payment requires a prior HMRC verification. This is not a one-off check: it must be re-run as part of the April 2026 due-diligence duty.
- Implement a payment run checklist. The CIS300 filing deadline (19th), the HMRC payment deadline (22nd) and the nil-return obligation all need to sit in the finance team's monthly calendar.
- Brief the relevant directors. Sections 62A and 62B, and the officer-liability rules behind them, make CIS compliance a personal matter for the individuals signing off payments. Directors should understand the exposure and the three due-diligence steps that manage it.
If you need help establishing whether your organisation has crossed the threshold, or want to set up CIS compliance from scratch, see the full range of what we do on our services page.