CIS Deemed Contractor Status: When a Property Business Has to Operate CIS on Its Own Spend

The Construction Industry Scheme is built for building firms, but it does not stop at the construction industry's front door. A landlord expanding a build-to-rent block, a housing association running a refurbishment programme, or a property investor commissioning a large conversion can all end up operating CIS on their own contractor payments — not because they are in construction, but because they have spent enough on it.

Who this catches

CIS ordinarily applies to businesses that are themselves contractors in the construction industry, paying subcontractors for construction work. But a second category exists alongside them: deemed contractors, businesses whose main activity has nothing to do with construction but which are pulled into the scheme anyway because of how much they spend on it. Government departments, local authorities and NHS bodies are deemed contractors automatically, regardless of spend. Everyone else — property investment companies, housing associations, retailers, and any other business paying for construction operations — is tested against a spending threshold instead.

For property businesses specifically, this most often catches landlords and investors who are growing quickly: a portfolio moving from occasional refurbishment into a genuine development programme, or a build-to-rent operator commissioning new blocks through main contractors, can cross into deemed contractor territory well before anyone thinks to check.

The £3 million rolling 12-month test

Since 6 April 2021, a business becomes a deemed contractor once its expenditure on construction operations exceeds £3 million within the previous 12 months. Crucially, this is tested on a rolling basis, not as a single once-a-year snapshot — a business needs to be watching its trailing 12-month construction spend continuously, because the threshold can be crossed mid-year, the moment a payment tips cumulative spend over the line, not on some fixed annual review date.

This replaced an earlier, more forgiving test that looked at average annual expenditure exceeding £1 million across the preceding three years. The rolling 12-month test catches a business faster, particularly one whose spend is lumpy — quiet for a couple of years, then a large single scheme that clears £3 million well within twelve months.

Once triggered, deemed contractor status does not simply lapse at the end of the project. HMRC's position is that it continues until construction expenditure for the trailing 12 months falls back under the threshold, which in practice means many property businesses with an ongoing pipeline of work stay registered and operating CIS continuously, rather than switching it on and off scheme by scheme.

Why group structures don't provide an escape route

Before the 2021 reform, some groups structured development activity across several separate companies specifically to keep each individual entity's spend under the threshold. That route was closed off deliberately: connected companies must now aggregate their construction expenditure when testing against the £3 million figure, so a group running several SPVs cannot avoid deemed contractor status simply by spreading the same total spend across more legal entities. If you are already managing a group of SPVs for the reasons covered in our guide to associated companies and marginal relief, the same connected-company logic now follows you into CIS — it is worth checking combined group construction spend, not just what any single SPV has committed to a contractor.

What "construction operations" actually covers

CIS applies to a broad definition of construction operations under the underlying legislation: general building and civil engineering work, site preparation, alterations, repairs, demolition, and the installation of systems like heating, lighting, power, water and drainage. It is not limited to ground-up new build — a substantial conversion, refurbishment or fit-out programme falls within it just as much as constructing a new block from scratch. Routine, minor maintenance sits outside the scheme, but the line between "maintenance" and "construction operations" is exactly the kind of judgement call that is worth getting checked before it is assumed away, particularly once spend on a wider programme of works is being aggregated toward the £3 million figure.

What registering as a deemed contractor actually involves

• Register with HMRC as a contractor, separately from any existing registration as a subcontractor if the business also does work for others.
• Verify each subcontractor with HMRC before making a first payment, to establish whether they should be paid gross, with 20% CIS tax deducted, or with 30% deducted where they cannot be verified.
• Deduct CIS tax from the labour element of payments to subcontractors who are not registered for gross payment, and pay those deductions over to HMRC.
• File a monthly CIS300 return, due by the 19th of each month, even in months where no subcontractor payments were made — a nil return is still required, and missing it triggers automatic penalties.
• Keep records of gross amounts paid, materials excluded from the deduction, and tax deducted, in the form HMRC expects to see if it asks.

None of this is exotic if a business already runs payroll and other tax compliance in-house, but it is a genuinely new monthly obligation for a property business that has never had to think about it before — and the penalties for late or missing CIS300 returns accrue in the same unforgiving way whether the business considers itself a "real" contractor or not.

The trap in expanding portfolios

The businesses most likely to miss this are the ones growing fastest. A landlord who has always paid a handful of local tradespeople for routine repairs does not think of themselves as a contractor, and has no reason to check a threshold they have never heard of — right up until a single large conversion or a build-to-rent scheme pushes trailing 12-month construction spend past £3 million. Because the test is rolling rather than annual, that can happen mid-project, with deemed contractor obligations starting from the point the threshold is crossed rather than from the start of the next tax year. Getting this wrong is not a paperwork footnote: operating without registering as a contractor when required, and failing to deduct CIS tax from subcontractors who should have had it deducted, exposes the business to HMRC assessment for the tax that should have been withheld, on top of the missed-return penalties.

Common mistakes

• Assuming deemed contractor status only applies to housing associations and public bodies, rather than to any business, including a private landlord or developer, that crosses the spend threshold
• Testing spend once a year rather than watching the rolling 12-month figure, and missing the point mid-year where the threshold was actually crossed
• Looking only at a single SPV's spend rather than the connected group's combined construction expenditure
• Treating a large refurbishment or conversion programme as "maintenance" and excluding it from the spend calculation
• Assuming deemed contractor status switches off automatically once a specific project finishes, rather than continuing until trailing spend genuinely falls under the threshold

If your business is scaling up construction activity — whether that is a build-to-rent pipeline, a portfolio-wide refurbishment programme, or a series of conversions run through connected SPVs — it is worth checking your position against the £3 million test before a contractor payment run gets ahead of your registration. Our Property Advisory service covers CIS alongside the wider tax structuring of a development programme.

Common questions

What is a CIS deemed contractor?

A deemed contractor is a business that isn't itself in the construction industry, such as a property investor, landlord or housing association, but which has to register and operate the Construction Industry Scheme on its payments for construction work because its spend on construction operations is high enough. Government departments, local authorities and NHS bodies are always deemed contractors regardless of spend; other businesses become deemed contractors only once they cross a spending threshold.

What is the CIS deemed contractor threshold?

Since 6 April 2021, a business becomes a deemed contractor once its expenditure on construction operations exceeds £3 million within the previous 12 months, tested on a rolling basis rather than as a single annual snapshot. This replaced the earlier rule, which looked at average annual expenditure exceeding £1 million across the preceding three years.

Does group company construction spend get combined for the £3 million threshold?

Yes. Since the April 2021 reform, connected companies must aggregate their construction expenditure when testing against the £3 million threshold, specifically to stop a group spreading spend across several SPVs to keep each one individually under the limit. A property group running multiple development or investment SPVs needs to look at combined group spend, not just what any single company has spent.

What does a deemed contractor have to do once registered?

Register with HMRC as a contractor, verify each subcontractor's payment status before paying them, deduct CIS tax at 0%, 20% or 30% depending on that status, pay the deductions over to HMRC, and file a CIS300 return every month even in months with no payments, alongside keeping the underlying records HMRC expects to see on request.

This article is general information, not personal tax advice, and tax rules change. Your own position depends on facts we cannot see from here — please take advice before acting on anything above.

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