The Construction Industry Scheme is one of those areas where mobile service business owners either know it inside out or have a vague sense they should probably look into it. The cost of being in the second camp is significant: HMRC can charge penalties for failing to register, failing to deduct, or deducting the wrong amount. The scheme applies to a broad range of construction operations - including installation work in electrical, heating, plumbing, roofing and similar trades - and the line between "this applies to me" and "this doesn't" is not always obvious. This is an overview of how CIS works and how to assess whether it applies to your business. It is not legal or tax advice - if you are uncertain about your position, speak to an accountant or contact HMRC directly.
This article is general information only and does not constitute tax or legal advice. CIS rules are specific to your circumstances. If you are unsure whether CIS applies to you - as a contractor, subcontractor or both - consult a qualified accountant or contact HMRC's CIS helpline (0300 200 3210).
What CIS Is and Why It Exists
The Construction Industry Scheme was introduced to reduce tax evasion in the construction sector, where subcontracting is common and it was historically easy for workers to disappear before paying their tax. Under CIS, a contractor (a business that pays subcontractors for construction work) must:
- Register with HMRC as a CIS contractor.
- Verify each subcontractor with HMRC before making the first payment to them.
- Deduct the correct amount from the subcontractor's payment for labour (not materials) and pay it to HMRC on their behalf.
- Submit monthly returns to HMRC showing what was deducted and from whom.
- Issue payment statements to subcontractors showing what was deducted.
Subcontractors receive their payment minus the CIS deduction. They then offset those deductions against their own tax bill at self-assessment (sole traders) or reclaim them through their company if they are limited companies.
The Three Deduction Rates
The deduction rate applied to a subcontractor depends on their registration status with HMRC:
| Subcontractor Status | Deduction Rate | How to Get This Rate |
|---|---|---|
| Gross payment status | 0% (no deduction) | Subcontractor applies to HMRC and meets turnover and compliance criteria |
| Registered with CIS | 20% | Subcontractor registered with HMRC under CIS but not yet at gross status |
| Not registered | 30% | HMRC cannot verify the subcontractor when the contractor checks |
The deduction only applies to the labour element of the payment. If a subcontractor invoices for both labour and materials, the deduction applies to the labour portion only. This is why subcontractor invoices should clearly separate labour and materials - and why contractors need to ask for that separation.
Note: Gross payment status is available to subcontractors who have been in business for a period, have a turnover above a threshold (currently £30,000 for sole traders), and have a clear tax compliance record. HMRC can also withdraw gross payment status if compliance slips.
What Counts as a "Construction Operation" Under CIS
CIS applies to "construction operations" as defined in the Finance Act 2004. The definition is broader than most people expect:
- Construction, alteration, repair, extension, or demolition of buildings and structures
- Installation of systems in buildings - including heating, lighting, air conditioning, ventilation, power supply, drainage, sanitation, water supply, and fire protection systems
- Groundwork, landscaping, and civil engineering work
- Painting and decorating of the exterior or interior of buildings
- Site preparation, scaffolding, and temporary works
- Cleaning buildings where done as part of construction or in preparation for occupation after a major build
For mobile service businesses, the key area is installation work. Installing a new boiler, fitting a new consumer unit, running new electrical circuits, installing a heating system, laying new drainage - these are all likely to fall within CIS.
What Is Excluded From CIS
Not everything in the trades falls under CIS. Excluded operations include:
- Drilling for oil or gas
- Mining and quarrying
- Manufacturing and delivery of materials (without installation)
- Architecture, surveying, and consulting
- Carpet fitting and other soft furnishing installation
- Signmaking and erection of signs
More relevant for mobile service businesses: routine repair and maintenance of existing systems can fall into a grey area. Servicing a boiler that is already installed, repairing an existing electrical fault, or unblocking a drain are often considered maintenance rather than construction operations. But the line between "repair" and "installation work incidental to a repair" is not always clear, and HMRC's guidance acknowledges the complexity.
The maintenance grey area
HMRC's view is that routine maintenance and repair of existing systems does not generally fall within CIS. However, if a repair involves significant installation work (replacing a significant portion of a system, installing new components as part of a broader job), it may cross into CIS territory. If you regularly do jobs that sit on this line, get an accountant's view on your specific work type.
Who Is a "Contractor" Under CIS?
Two types of business fall within the CIS contractor definition:
For a typical mobile service business, the more common scenario is being a subcontractor receiving CIS deductions - for example, a heating engineer subcontracted by a property developer or main contractor. But if you in turn hire subbies for your own jobs, you become a contractor and take on the deduction obligations for those payments.
The Cost of Getting It Wrong
HMRC's CIS penalties are structured around the monthly return obligation:
| Delay | Penalty |
|---|---|
| 1 day late | £100 |
| 2 months late | Additional £200 |
| 6 months late | Additional penalty - greater of £300 or 5% of CIS deductions due |
| 12 months late | Further additional penalty - same structure, potentially higher |
Failing to deduct when required - or deducting at 20% when the subcontractor is unregistered (and should be 30%) - means HMRC can pursue the contractor for the shortfall, regardless of what has already been paid to the subcontractor.
Practical Steps If You Think CIS Applies to You
- Assess your work type honestly. If you regularly do installation work - new systems, significant new wiring, new heating - CIS is likely to apply to subcontracted labour on those jobs.
- Register as a contractor with HMRC if you pay subcontractors for CIS-qualifying work. Registration is done online through your HMRC business tax account.
- Register as a subcontractor if you are paid by contractors for CIS work. Even if you only ever receive work from one contractor, register to ensure you are deducted at 20% rather than 30%.
- Verify subcontractors before paying them. Use HMRC's online verification service to check each subcontractor's status and the correct deduction rate.
- Separate labour and materials on invoices - both on the invoices you issue to contractors and on those you receive from subbies.
- Submit monthly returns on time. Even a nil return (no CIS-qualifying payments that month) must be submitted or notified to HMRC.
- Issue payment statements to subcontractors. Each payment that has had CIS deducted requires a written statement showing the gross amount, deduction and net amount paid.
Bottom Line
CIS applies to more mobile service businesses than many owners realise. If you do installation work, or subcontract labour for installation work, the scheme is likely relevant to you. The penalties for non-compliance are automatic and can accumulate quickly. The obligations - monthly returns, verification, correct deduction rates - are manageable with the right process in place, but they do require a system rather than informal tracking.
If you are unsure whether CIS applies to your specific business and work type, the most straightforward step is to speak to an accountant familiar with the trades sector, or call HMRC's CIS helpline directly. The cost of finding out is negligible compared with the cost of getting it wrong over several years.
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