Most subcontractors know that CIS applies when working for building companies. What the majority do not know is that CIS also applies when working for organisations that have never built anything — if they spend enough money on construction each year. One piece of legislation. An enormous financial blind spot.

The £3 Million Rule Nobody Tells You About

HMRC's Construction Industry Scheme was designed for the building trade. But Parliament built in a clause that captures organisations far outside it: the Deemed Contractor rule.

It works like this. Any business or public body — regardless of what sector they operate in — becomes a contractor under CIS if their spend on construction operations exceeds £3 million in any rolling 12-month period. Cross that threshold, and they are legally required to register for CIS and deduct tax from every qualifying subcontractor on their books.

Who Qualifies? More Organisations Than You Think

The list of Deemed Contractors is broader than most subcontractors imagine. If you have ever worked for any of the following, CIS may have applied — whether you knew it or not:

The Real Cash Flow Hit

Here is what happens in practice. A heating engineer quotes £10,000 for a boiler upgrade at a council-managed property block: £7,000 labour, £3,000 materials. The council is a Deemed Contractor. Their accounts department applies CIS deductions to the labour portion.

How to Protect Yourself: A Practical Checklist

• 01
  Ask Before You Quote — Not After You Invoice Before accepting any job from a large organisation, ask directly: "Are you registered as a CIS contractor or Deemed Contractor?" A simple question at quote stage prevents a nasty surprise at payment stage. If they are unsure, assume they are.
• 02
  Always Itemise Labour and Materials Separately CIS deductions apply only to the labour element of your invoice — not materials. An invoice that lumps everything into one total line gives the Deemed Contractor grounds — or an excuse — to deduct from the full amount. Split every invoice clearly: labour line, materials line, VAT line.
• 03
  Confirm Your CIS Registration Is Active If a Deemed Contractor cannot verify you in HMRC's system, they are legally obligated to deduct at 30%. Check your registration is live, your UTR is correct, and your name matches exactly what HMRC holds on file. Do this before the first job — not after the first payment shortfall.
• 04
  Request a Payment and Deduction Statement Every Time For every job where CIS is deducted, you are entitled to a Payment and Deduction Statement from the Deemed Contractor. This is the document you need to reclaim your deductions through Self Assessment. Do not let a job close without one — if the organisation fails to issue it, you have very limited recourse when filing your return.
• 05
  Price It In — Or Negotiate Net Terms If you know a client is a Deemed Contractor, factor the cash flow gap into your quote. The 20% withheld is recoverable through your tax return — but not until months later. Either price to absorb the wait, or negotiate payment on account terms so the deduction does not strand your working capital mid-project.

Quick Rule of Thumb: Who to Watch For

You cannot always know upfront whether a client crosses the £3 million threshold. But you can apply a simple default that protects your cash flow in almost every case.

The One Question That Saves You Every Time

The Deemed Contractor rule is not obscure legislation buried in HMRC guidance that only accountants read. It is a live obligation that affects thousands of subcontractors working for public bodies and large organisations every week — most of whom have no idea it exists until the money is already missing from their invoice.

The fix is a single sentence asked before the job starts: "Are you registered for CIS as a contractor?" Four seconds of conversation that can protect hundreds of pounds per job — and ensure you have the paperwork to reclaim every penny of deductions through your Self Assessment when the tax year closes.