CIS for established construction firms becomes a system of compliance pressure points rather than a single regime. Gross Payment Status, where held, is a 30% margin difference: lose it and competitive bidding becomes harder, supplier relationships strain, and cash flow tightens. Deemed contractor status pulls non-construction businesses into CIS without their realising. Mixed supply-and-fit contracts split into different tax treatments at the line-item level. Intermediary chains and umbrella structures create cascading liability. And HMRC pursues each of these with formal compliance reviews.
This guide covers the senior compliance issues for principal contractors and substantial subcontractors. Each section links to a detailed companion piece on the specific issue.
GPS withdrawal happens fast and recovery is slow
A single late filing or payment in any of the seven compliance categories (Self Assessment, Corporation Tax, PAYE, CIS300, VAT, plus two others depending on the structure) can trigger GPS withdrawal. Reapplication requires 12 months of clean compliance plus formal scheme. The cash-flow impact during the GPS-withdrawn period is typically tens of thousands per month for a substantial subcontractor.
The GPS compliance test in detail
GPS holders are subject to an annual review of their compliance over the preceding 12 months. The test is mechanical and unforgiving. The categories tested:
- 1Self Assessment returns and payments (where applicable to the holder).
- 2Corporation Tax returns and payments.
- 3PAYE returns (RTI) and payments.
- 4CIS300 monthly returns and CIS payments due.
- 5VAT returns and payments where the holder is registered.
- 6Class 1 NIC payments where applicable.
- 7PAYE settlement agreements where in place.
A failure in any one category is a failure of the test. HMRC notifies the holder of withdrawal in writing, with appeal rights and a 30-day window. The withdrawal takes effect at a defined date; from that date, all payments to the subcontractor are made under deduction at 20% (or 30% if not separately CIS-verified).
Mixed supply-and-fit contracts
Where a contract combines supply of materials and installation, the CIS treatment splits at the line-item level:
- Pure supply of materials (no installation): outside CIS scope.
- Pure installation labour with no material element: full CIS deduction on the labour.
- Combined supply and fit: CIS applies to the labour element only; materials element is separated and not subject to CIS.
The split is documented in the payment certificate. Errors in either direction (treating mixed contracts as pure labour, or pure supply where there is in fact a labour component) create CIS exposure on either side. Subcontractors who handle their own splits often inadvertently understate the labour component to reduce deduction; HMRC compliance reviews catch this routinely.
Deemed contractors — the £3 million threshold
Non-construction businesses that spend more than £3 million on construction operations in any rolling 12-month period become "deemed contractors" and have to operate CIS as if they were construction businesses. This catches:
- Property investors with substantial development or refurbishment programmes.
- Retailers expanding their store estate.
- Manufacturers undertaking factory expansions.
- Local authorities and other public bodies (where not otherwise exempt).
- Hospitality groups undertaking refurbishment programmes.
The threshold is rolling and triggered by spend, not by activity classification. Deemed contractors must register with HMRC as contractors, verify subcontractors, deduct CIS where applicable, and file CIS300 returns monthly. Late notification of deemed contractor status creates back-deduction exposure.
Property investors versus property developers
A property investor (holding for rental income) is generally outside CIS even when commissioning construction work; a property developer (building for sale) is inside CIS as an end client. The line is not always obvious — a buy-to-let landlord doing a substantial refurbishment plus partial sale of the portfolio can fall on either side depending on intention and execution. Get this characterisation right before any commitment.
Intermediaries, umbrellas, and cascading liability
CIS responsibility cascades down the supply chain. A principal contractor paying a labour-only intermediary is responsible for verifying that intermediary; the intermediary then has its own CIS obligations downstream. Umbrella companies adding a layer of administrative employment further complicate the position.
HMRC scrutinises intermediary structures aggressively. Where the structure is judged to be an artificial arrangement to avoid CIS or PAYE, transfer-of-debt provisions can place the original principal contractor liable for the underlying tax. The Managed Service Company legislation, IR35, and the agency rules all interact in this space. Any structure involving more than a single layer between the principal contractor and the worker should have specialist review.
Recovering CIS deductions when a counterparty fails
Where a contractor that has deducted CIS from your subcontractor payments enters administration or liquidation before remitting to HMRC, the CIS deductions become a complicated cash recovery position. Routes:
- 1Standard claim through the administrator/liquidator as an unsecured trade creditor for the deduction amount.
- 2For company subcontractors: claim against PAYE liability of own payroll via Employer Payment Summary.
- 3For sole traders: offset on Self Assessment for the year, with any excess refundable.
- 4In specific circumstances: argue for HMRC trust treatment of unremitted CIS as Crown debt rather than ordinary trade debt.
GPS at risk or CIS dispute open?
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