Introduction

A property investment business has spent £3.2 million refurbishing offices and rental units in the past year. Nobody calls it a construction company. Its accounts team books the costs to property improvements, pays builders in full and files no CIS returns. Then an adviser asks whether the business has crossed the deemed contractor threshold.

The answer cannot be found from its industry label alone. Some developers are mainstream CIS contractors because construction is part of their trade. Other organisations, including some property investors and landlords, may become deemed contractors only after passing the expenditure test. Even then, the treatment of individual payments requires a separate assessment.

This guide explains mainstream versus deemed contractors, the rolling £3 million test, construction operations, own-premises exceptions, registration and what to do if CIS should have been operated earlier.

A business can incur CIS contractor obligations without calling itself a building contractor. Property owners, landlords and organisations making substantial construction payments should distinguish two very different routes into the Construction Industry Scheme: carrying on construction as part of their business and meeting the deemed-contractor expenditure test. Confusing them can create late registration and historic deduction problems.

Mainstream versus deemed contractors: the first decision

A property developer may be a mainstream contractor; the £3 million test is for qualifying non-construction businesses.

Because the distinction turns on the actual construction activities, assess it against HMRC’s CIS 340 guide rather than assuming that the £3 million test applies to every property developer.

HMRC lists builders, labour agencies and property developers among mainstream contractors where their business includes construction operations and they pay subcontractors. A development company should not wait until it spends £3 million if its activities bring it directly into mainstream CIS.

A company whose underlying business is not construction—such as a commercial property investor undertaking occasional major works—may instead become a deemed contractor. The legal classification follows activity and expenditure, not the wording on Companies House or the name of the nominal code.

The £3 million rolling expenditure test

The current deemed-contractor threshold is more than £3 million of construction expenditure over a relevant rolling 12-month period.

Monitor the rolling period as expenditure accumulates rather than checking only annual accounts. The statute and HMRC guidance provide the relevant calculation rules, including the timing of payments and construction expenditure included. A budget forecast should trigger earlier review when the business is likely to cross the threshold.

Consider a property group company with £1.45 million of qualifying refurbishments, £1.2 million of building work and £650,000 of further construction expenditure in one rolling 12-month period. Its £3.3 million total indicates that the threshold has been exceeded, subject to the legal classification of the spending. Do not automatically aggregate unrelated legal entities for the threshold without analysing the applicable rules.

For a simple numerical comparison, Illustrative 12-month qualifying expenditure: £1,450,000 + £1,200,000 + £650,000 = £3,300,000.

What counts as construction expenditure

Construction work can include site preparation, building, alterations, decorating and qualifying repairs.

Invoice titles are unreliable proxies for the CIS rules. A property ledger may use a single “repairs and maintenance” code for works that include building operations, cleaning, facilities services and other activities; some may be within CIS and others may not. The underlying scope of work is the critical evidence.

Ask project teams to classify work packages by the nature of the operations, contractor type, site, commitment date and amount. Building contracts, purchase orders, invoices and completion documents will be more useful in an HMRC review than a year-end spreadsheet containing unexplained totals.

Landlords, property developers and investment portfolios

Landlords are not automatically CIS contractors, and not all property developers should be tested as deemed contractors.

Landlord and development businesses need reconciled project records; our property accounting support covers the underlying rental and development accounting workflows.

Rental income alone does not create CIS contractor status. However, landlords whose businesses make substantial construction payments need a mainstream-or-deemed assessment. The correct answer depends on what the company actually does and, for deemed contractor status, its qualifying expenditure.

A property development company building dwellings for sale can be mainstream. A commercial landlord holding a rental portfolio and carrying out a large refurbishment programme may instead have to monitor the £3 million test. A single person can also operate different businesses with different facts; avoid blanket classifications across a portfolio.

Own-premises exceptions and investment property

Some payments for construction on premises used for the deemed contractor’s own business can be outside CIS.

HMRC’s own-premises exceptions should not be confused with the expenditure test. Certain spending can count towards the threshold but the eventual payment may fall within an exception. A warehouse a retailer occupies for its own trade is different from an investment building let to third parties.

Before treating a payment as exempt, record who occupies the building, the purpose of the work and the relevant statutory exception. Property held as a rental investment generally should not be assumed to qualify merely because the landlord legally owns it.

Registering and operating monthly CIS

Where CIS applies to payments, the business must register, verify subcontractors, deduct correctly and submit relevant monthly returns.

Once relevant payments fall within the scheme, outsourced CIS return preparation can support verification, deduction statements and monthly reconciliations, with the UK adviser retaining final control.

Operational controls include collecting verified UTR details, confirming the 0%, 20% or 30% rate, separating materials in the payment calculation, filing CIS300 returns and providing deduction statements within the statutory deadline. Only payments within scope should be included; ordinary supplier payments should not be drawn into CIS merely because they relate to a property.

Designate one owner of the construction expenditure tracker and a second owner of payment processing. At each month-end, reconcile project costs and relevant subcontractor liabilities to the CIS reporting ledger.

What to do if a deemed contractor registers late

First reconstruct when the relevant status arose and which payments were actually within CIS.

An accountant should build a timeline: qualifying rolling spend, date threshold passed, construction contracts, payments, verification history and returns submitted. That timeline helps distinguish late registration from missed deductions or filing errors.

HMRC penalties may arise for late returns, and amounts not deducted can create additional exposure. Disclose and rectify problems promptly using documented calculations rather than retroactively assuming every payment was subject to deduction. Where the facts are disputed, consider obtaining specialist advice.

An accounting control framework for property clients

A rolling project-level schedule catches CIS risk earlier than an annual financial-statement review.

For projects involving multiple trades, construction sector accounting helps make threshold monitoring and contractor reporting part of the same month-end process.

Create a construction cost category with subcodes for qualifying operations, clearly out-of-scope services and items requiring review. Record site, project, supplier, payment date and whether a payment exemption is claimed. Add a rolling 12-month pivot or report to each management pack when expenditure approaches the threshold.

For UK accountancy practices supporting developers and landlords, outsource recurring verification, CIS300 preparation and reconciliations while the lead adviser retains responsibility for the classification and advice. Probal Global’s construction and CIS outsourcing services align with this split.

Three questions that identify scope quickly

Does the company carry on construction as part of its ordinary business? If yes, assess mainstream contractor obligations first. If not, how much qualifying construction expenditure has it incurred over the relevant rolling 12 months? If deemed status arises, which actual payments are within CIS after considering relevant exceptions? Each question requires separate documentation.

A property portfolio dashboard

Useful management-pack fields are site, legal owner, development versus investment purpose, payment date, supplier, construction operations category, amount included in the rolling threshold and CIS status of the payment. The dashboard should distinguish forecast spend from actual payments to prevent incorrect conclusions.

Why this matters to UK accountancy practices

The benefit is not another list of rules. It is a consistent process that links source documents to reporting, exposes exceptions before deadlines and produces a concise working paper for the senior reviewer. The practice retains responsibility for technical judgement, client advice and final approval. The bookkeeping or preparation team should never guess at a legal classification simply to complete the monthly file.

Probal Global positions its services as an extended back-office team for UK firms. The practical outsourcing boundary is clear: transaction processing, schedules, reconciliations, return preparation and exception tracking can be delegated; fact-sensitive tax decisions, client instructions and final sign-off remain with the appointed adviser.

Worked example: monitor the test across a property portfolio

Assume a property group has one company operating a development trade and a second company holding completed investments. The development company may already be a mainstream contractor. The investment company must consider whether its own relevant construction expenditure exceeds the deemed contractor test. The answer cannot be reached by adding both companies’ spending and applying one classification to the group without analysing the rules for each entity.

For the investment company, create a rolling 12-month schedule of qualifying construction expenditure. Record the project, supplier, nature of works, date, amount and classification. Review the schedule at every month-end and flag when planned works could push expenditure above £3 million. Once the business becomes a deemed contractor, assess each subsequent payment on its own merits, including relevant exemptions.

Frequently asked questions

What is a deemed contractor?

A non-mainstream construction organisation brought within CIS through the statutory construction expenditure conditions.

What is the current threshold?

More than £3 million of relevant construction expenditure over a rolling 12-month period.

Are developers always deemed contractors?

No. Developers whose business involves construction operations may be mainstream contractors.

Are landlords automatically within CIS?

No. Their business activity and construction spending determine whether and how CIS may apply.

Do repairs count towards construction expenditure?

Some repairs are construction operations; assess what work was actually carried out.

Does spending on owned premises count?

It can count towards the expenditure test even if an exception applies to certain payments.

What if the business missed CIS registration?

Reconstruct the status timeline and in-scope payments, then consider corrections and disclosure.

Can an accountant outsource CIS processing?

Yes, including verification, monthly returns, statements and reconciliation; retain technical sign-off internally.

Does the £3 million test reset at the financial year end?

No. The test uses a rolling 12-month measure, so expenditure must be monitored throughout the year rather than only when annual accounts are prepared. A property business can cross the threshold between reporting dates, especially when several refurbishment projects overlap.

Is a landlord exempt from CIS on repairs to rental property?

Not simply because it owns the property. The classification depends on whether the landlord is a mainstream or deemed contractor, whether the work constitutes construction operations and whether the particular payment qualifies for an exemption. The own-premises exemption is not a blanket exemption for investment or let property.

How Probal Global supports UK accounting practices

The costly mistake is not necessarily making a large construction payment. It is making that payment without first deciding whether the entity and payment fall within CIS. Property advisers can make the scheme manageable by tracking qualifying expenditure monthly, distinguishing mainstream and deemed status and keeping exemptions evidenced.

For firms carrying this work across multiple clients, the preparation challenge is maintaining clean source data, reconciled balances and an audit trail that the UK reviewer can follow. Probal Global supports UK accountancy practices as a back-office preparation team. The firm retains the client relationship, professional judgements and final sign-off; the outsourced work is built around its existing process and software.

Explore our relevant services: construction industry accounting  •  property accounting  •  CIS returns

Related article links below are scheduled for activation when their destination articles are published:

Related reading: Cis Gross Payment Status  |  Cis Deduction Statements

This article provides general UK accounting and tax information at 4 November 2026 and is not a substitute for advice tailored to an individual business. Specific contractual, regulatory and HMRC facts should be checked before action.

Authoritative references

·        HMRC — who is covered by CIS

·        HMRC — deemed contractor rules

·        HMRC — CIS 340