CIS for subbies in 2026: how tracking mistakes cost UK tradespeople thousands

A subbie spent 46 weeks doing labour for a major UK contractor. Paid £400 a week in cash. He went into his self-assessment expecting a chunky refund. The contractor had been deducting 20% under CIS the whole time. £4,600 owed back.

HMRC said no. They checked with the contractor. The contractor's records didn't show him as a subbie at all. No monthly CIS300 return ever mentioned him. He'd been "verified" with HMRC for the first time two years later. His own accountant, the one who'd kept all the paperwork, had died. The contractor was, in the tribunal's words, "unhelpful" with information requests.

The tribunal ruled against him. He had no payment and deduction statements to prove anything. The £4,600 was gone. He'd done the work, the deductions had probably happened in some form, but on HMRC's books there was no trail. Sonny Joseph McEwen v HMRC [2015] UKFTT TC04677 isn't a famous case. It's just one of hundreds where a sole trader lost real money because someone else's record-keeping was a mess.

If you're working as a subbie under the Construction Industry Scheme in the UK in 2026, this article is the one I wish someone had handed me when I started. It's not legal advice. Speak to an accountant for that. But it's what I'd want a mate to know before the next tax year ended.

What CIS actually is, in plain English

The Construction Industry Scheme is a tax-collection mechanism HMRC bolted on top of UK construction in the 1970s and tightened in 2007 and again in 2024. The reason it exists is simple: construction has historically been the easiest sector to dodge tax in. Cash jobs, subbies coming and going, vans crossing county lines. So HMRC made the contractor collect the tax at source, before the subbie ever sees it.

Here's the mechanic in one paragraph. When a contractor pays you for labour, they're required to verify you with HMRC first. Verification spits back one of three deduction rates: 0% (you've got gross payment status and they pay you the full whack), 20% (you're registered with HMRC and that's the standard rate) or 30% (you're not registered or HMRC can't find you). They take whatever rate applies, pay HMRC, and pay you the rest. Then once a month, by the 19th, they file a CIS300 return listing every subbie they paid and how much they deducted.

That deduction is not your final tax. It's an advance payment. When you file your self-assessment at the end of the year, HMRC adds up everything that was deducted from you, subtracts your actual tax bill (which factors in your expenses, personal allowance, the lot), and the difference comes back as a refund. Or, if you owed more, you pay the difference.

That's the theory. The practice is where it goes sideways.

The £100 penalty that quietly becomes £6,000

This bit's for the contractors reading. Anyone subbing work out, even occasionally, even just one mate. If you've engaged anyone as a subcontractor in the past 12 months, this applies to you.

HMRC's penalty regime for late CIS300 returns is one of the cleanest examples of compounding I've ever seen, and not in a good way. It's set out in Schedule 55 of the Finance Act 2009, which is the same framework that catches late self-assessment returns. Here's how it stacks for a single missed monthly return:

• Day 1 late: automatic £100 penalty. Not a warning. Not a notice. A bill. Generated by HMRC's computer at one second past the deadline.
• Two months late: another £200 added. You're at £300 for that one return.
• Six months late: the bigger of £300 or 5% of the CIS deductions owed for that month. Plus daily penalties of £10 a day can kick in (capped at £900 across 90 days).
• Twelve months late: up to £3,000, or up to 100% of the CIS deductions on that return if HMRC decides the failure was deliberate.

Now here's the bit that floors people. Penalties are charged per return, not per business. Say you forgot CIS existed for half a year, which is more common than you'd think, and you've missed six monthly returns. You don't get one penalty chain. You get six. Six separate £100 penalties. Six separate £200 add-ons. Six separate everything. The numbers compound fast.

If you never paid any subbies in a given month, you might think you owe nothing. Wrong. Sort of. Before April 2015 you'd have been hit with a £100 penalty for a missing "nil" return. HMRC backed off that rule, so missing a nil return doesn't generate an automatic penalty any more. But you still need to either submit the nil return or formally tell HMRC you've stopped using subbies, otherwise they keep expecting one and the system gets confused.

One more wrinkle the books rarely mention. If HMRC decides the underpayment was "careless" rather than honest, their discovery assessment window stretches from 4 years to 6 years. If they decide it was deliberate, it stretches to 20 years. So a small bookkeeping shortcut you took in 2024 could come back at you in 2044.

The bigger story: HMRC is coming for construction harder than ever

This isn't theoretical. Everything above has always been on the statute book. What's changed in 2026 is the appetite to actually enforce it.

In the first six months of the 2025-26 tax year alone, HMRC raised over £15 billion through compliance activities. Construction is named explicitly as one of the priority targets. The Treasury has funded 5,500 additional compliance staff, specifically to extract more from sectors with historically poor compliance. There's no sector with a longer compliance rap sheet than construction.

In April 2026, HMRC broadened its CIS fraud powers. Contractors caught running dodgy CIS arrangements now face: loss of gross payment status for at least five years, full personal liability for the tax that should have been deducted, and personal penalties of up to 30% on top. That last bit is new. It means directors of limited companies can be pursued individually, not just the company. You can't liquidate your way out of it.

Industry data backs it up. Hudson Contract, who pay more self-employed tradespeople than anyone else in the UK, reports a sharp rise in HMRC compliance checks on construction SMEs through 2026. The cases they're seeing aren't dramatic fraud. They're well-run, successful companies being caught out on technical breaches: poorly-drafted subcontractor agreements, scaffolders claiming material deductions on kit they own outright, contractors who under-deducted because their verification was out of date.

The point isn't to scare anyone. It's to make clear that "I'll sort it later" is not a defensible plan in 2026.

Four ways UK subbies quietly lose money under CIS

Most CIS losses aren't dramatic. There's no court case, no penalty notice, no big bill. The money just never arrives. Here are the four most common ways it disappears.

1. The missing-statement problem

Every month you do work for a contractor, they're legally required to give you a payment and deduction statement. Most people call it a PDS. It shows how much they paid you, how much they deducted under CIS, and crucially, your verification reference. That PDS is the only evidence you have that the deduction happened.

Half the contractors out there forget. Some send them six months late. Some never send them at all. If you don't have a PDS for a particular month, you can't claim that deduction back on your self-assessment with any confidence. HMRC will want to verify it against the contractor's own CIS300 returns.

And here's the bit that's got worse recently. Up until 2024, if you couldn't get a PDS out of your contractor, you could ring HMRC's CIS helpline and ask them to dig it out of their records. As of July 2024, that helpline service has been withdrawn. You now have to write to HMRC PT Operations by post, including your UTR, the relevant tax years, and the contractor's details. Then you wait weeks. While the four-year claim clock keeps ticking.

2. The mismatch nobody tells you about

Your PDS from the contractor says they deducted £600 from you in May. You put £600 on your self-assessment. HMRC checks their own database. The contractor's CIS300 return for May doesn't list you at all. Or it lists you but for a different amount. Or it lists you under a slightly different UTR because the contractor mis-typed it during verification.

This is exactly what destroyed the McEwen claim at the start of this article. He had what he believed was the right amount in his head; HMRC had a contractor's database showing nothing. The tribunal sided with the database, not him.

You won't usually find out there's a mismatch until you've already filed and HMRC pauses your refund pending verification. By then the contractor might have changed software, gone limited, gone bust, or just got tired of your calls.

3. The four-year cliff edge

Sole traders have four years from the end of the tax year to claim back overpaid CIS. After that, the money's HMRC's forever. There's no extension. There's no "I didn't know" exception.

In one published case from an accountancy firm, a roofer turned up with four full years of unclaimed CIS refunds sitting at HMRC. He'd been registered, he'd been having 20% deducted on every job for years, and he'd never once filed a self-assessment that claimed it back. He got the most recent three years processed. The fourth year? Gone. That's typically thousands of pounds per year for a working subbie. Five-figure totals are common.

The four-year clock is the silent killer. Most people don't think of CIS as a thing they can lose by inaction. It is.

4. The "deducted on materials" trap

Under CIS, the 20% deduction is supposed to come off the labour portion of your invoice only. Materials are exempt. So say you invoice a contractor for £2,000, with £1,200 of that labour and £800 materials. The deduction should be 20% of £1,200, which is £240. Not 20% of £2,000.

Plenty of contractors, especially smaller ones, just apply 20% to the gross invoice total. That's £400 deducted instead of £240. You're losing £160 per invoice. Over a year of regular work, that's hundreds, sometimes thousands. You can claim it back at self-assessment, but only if you've kept invoices that clearly split labour from materials.

It works the other way too, by the way. If you're a scaffolder claiming a material deduction for the scaffolding you already own outright, HMRC's compliance teams are specifically targeting that pattern. Materials only counts when the materials were actually purchased for the job. Plant you own and bring with you is labour.

What tracking CIS properly actually looks like

Here's the discipline. It's not complicated, but it has to be relentless.

For subbies:

• Get every PDS in the same place, every month. Doesn't matter if it's a folder of emails, a shoebox of paper, or a database. But it has to be one place, organised by month and contractor, and reconciled against your actual invoices.
• Chase missing PDSs immediately, not at year-end. If you finished a job in May and you haven't got a PDS by mid-June, that's the time to ask. Six months later your contractor will have switched accountants twice.
• Reconcile the numbers monthly. Your invoice said you should have been deducted £240. The PDS says £400. That's a conversation to have this week, not next March.
• Keep a running total of CIS suffered. Year-to-date, month-by-month. So you know what you're owed back well before you sit down with self-assessment.
• File your self-assessment as early as possible after 6 April. Refunds from April to June filings often land within 4 weeks. Refunds from January filings can take 8 to 12 weeks because of the backlog.
• Check the labour-vs-materials split on every invoice you send. Make it explicit. A contractor who applies 20% to the gross is harder to challenge if your invoice didn't separate the two.

For contractors subbing work out:

• Verify every subbie before you pay them, every time. Even if you've used them before. Verification status can change between jobs.
• File the CIS300 monthly. Always. Even nil months. The 19th of the following month is the deadline. Set a recurring reminder, or use a tool that does it for you.
• Issue PDSs to every subbie within 14 days of the end of the tax month. Not on request. Automatically. That's the legal requirement.
• Don't apply CIS to the gross. Split labour and materials. Get this wrong and you'll be writing apology emails to your subbies and chasing reconciliations forever.

Why we built CIS handling into Trade PA the way we did

Honest answer: because I got it wrong when I was running a small building firm myself, and I lost real money I couldn't get back. PDSs missing, reconciliation done at the last minute, deductions I never properly checked. Standard tradie experience.

When we built Trade PA, CIS wasn't a feature we tacked on. It was one of the first things, because it's where so many sole traders lose money silently. The system stores PDSs against the contractor they came from, runs your monthly reconciliation automatically, alerts you if a PDS hasn't arrived when it should have, and generates the CIS section of your self-assessment from the actual records, not from your memory of what was deducted.

That's not magic. It's just what good CIS tracking looks like when it isn't being done in evenings on a knackered laptop. Whether you use Trade PA or not, the principle stands: every PDS in the same place, reconciled monthly, claimed early. If you don't, you'll join the long list of subbies who've quietly handed HMRC an interest-free loan for years and forgotten about it.

The 2026 enforcement climate is what it is. The penalty regime hasn't changed in 15 years. The 4-year claim window has been there since the scheme started. What changes is whether you're treating CIS as something that runs in the background of your business, or something you'll deal with later, every year, until the year you don't.

Trade PA