The April 2026 CIS reforms: what every UK builder needs to check this week

The Construction Industry Scheme changed on 6 April 2026. If you pay subcontractors, the old "verify once, trust your gut" approach is now a direct route to penalties that can end your business.

The reforms are the biggest overhaul since the scheme was modernised in 2007. HMRC's message is blunt: CIS compliance is no longer a monthly box-ticking exercise. It's a governance issue with personal liability for directors.

Here's what changed, what it means in practice, and what you need to do this week.

What's new from 6 April 2026

Four changes matter. In rough order of severity for builders using subbies:

1. Supply chain liability. HMRC can now penalise you for fraud committed by a subcontractor you hired — if they decide you "knew or should have known" something was off.
2. Immediate Gross Payment Status loss. If you fail that test, HMRC can strip your GPS on the spot and charge a penalty of up to 30% of the payment.
3. Five-year GPS reapplication ban. Lose GPS under these rules and you can't reapply for five years. The old ban was one year.
4. Mandatory nil returns return. If you filed no CIS payments in a month, you must now file a nil return (or pre-notify HMRC of inactivity). The full late-filing penalty regime is back.

There's a fifth change — payments to local authorities and certain public bodies are now fully outside CIS. Good for public-sector work, largely irrelevant for residential and commercial builders.

"Knew or should have known" — what this actually means

This is the one that'll catch builders out. The legal test is borrowed from VAT law (the Kittel test, if you want to look it up) and it's ruthless.

HMRC doesn't have to prove you knew a subcontractor was dodgy. They only need to show that a reasonable business in your position should have realised there was a risk. It's an objective test. Your intent doesn't matter. "I didn't know" is not a defence.

What counts as a red flag HMRC might argue you should have spotted:

• A subcontractor offering rates that are too cheap for the work
• Sudden changes to the payee bank account, especially to a third party
• VAT numbers that don't verify
• A subbie with no verifiable trading history asking for cash
• Paperwork that doesn't match reality on site
• A CIS verification that fails but the trade pressures you to pay anyway

Losing GPS — the cash flow earthquake

If you hold Gross Payment Status, it means customers pay you in full without deducting CIS. You handle your own tax. It's the default for any serious contracting business because without it, your customers deduct 20% from every invoice — that's a fifth of your cash gone the moment it lands, reclaimed months later through your self-assessment.

Under the new rules, if HMRC decides you failed the "knew or should have known" test, they can revoke GPS immediately. Not after an appeal. Not after a hearing. Immediately.

The moment that happens:

• Every main contractor you work for must start deducting 20% from your invoices
• Your cash flow collapses by a fifth overnight
• You're barred from reapplying for GPS for five years
• In some cases, directors can be held personally liable

For most mid-sized building firms, this is existential. The old one-year ban was survivable. A five-year ban, for most contractors, is not.

Nil returns — the silent penalty trap

This one's more administrative but catches people out. Before 2015, if you had no CIS payments to report in a month, you still had to file a nil return. That requirement was removed — supposedly to reduce admin — but ended up generating loads of late-filing penalties when contractors forgot to flag periods of inactivity.

As of 6 April 2026, nil returns are back. If you don't pay any subcontractors in a given month, you must either:

• File a nil return on time, or
• Pre-notify HMRC of a period of inactivity (up to 6 months)

Miss it and you're looking at an initial £100 penalty, another £100 at 2 months, £300 or 5% of any liability at 6 months, and a further penalty at 12 months. Contractors who go quiet for a few months between projects are the ones who'll get stung.

What you need to do this week

Practical actions, in order:

1. Re-verify every active subcontractor. Go through HMRC's CIS portal and confirm status on every subbie you're currently paying. Don't assume the status from three months ago still applies.
2. Document your onboarding process. If HMRC investigates, you'll be asked what due diligence you did. "I had a chat on the phone" isn't a record. Write down what you check: CIS status, UTR, bank verification, insurance, photo ID.
3. Red-flag check your supply chain. Is anyone offering rates that seem too low? Anyone asking for cash? Anyone whose bank account has changed recently? These are the relationships to scrutinise first.
4. Set a calendar reminder for the 19th of every month. This is the CIS return deadline. If you're not paying subbies that month, file a nil return or pre-notify inactivity. Don't forget.
5. Review your contracts. Your subcontractor agreements should now include explicit anti-fraud warranties and audit rights. If they don't, update them.
6. Keep records for at least three years. HMRC can request them at any time and failure to produce can cost up to £3,000 per occurrence.

Or: make it someone else's problem

There's a different way to approach this, which is to stop being the CIS contractor in the first place.

Under HMRC's rules, the CIS obligation sits with whoever makes the payment to the subcontractor. If you book your trades through Cabin, we're the one paying — so we're the CIS contractor on that engagement, not you. Your exposure to all of the above is zero.

That means:

• No verifications to run — we verify every trade before their first booking
• No monthly returns to file for Cabin-booked trades — we file them
• No deduction statements to issue — we issue them
• No "knew or should have known" exposure — that risk sits with us
• No supply chain liability — that risk sits with us
• No GPS at stake — your GPS is untouchable for Cabin-booked work

Cabin also handles the GPS clock-in, verifies identity, collects insurance details, and holds the audit trail HMRC will eventually ask to see. The trade gets paid same-day on completion (CIS already deducted and paid to HMRC on your behalf). You get one invoice from Cabin per booking and your CIS exposure on that relationship is extinguished the moment you pay it.

For builders still paying trades direct, the April 2026 reforms are a serious tightening of the screws. For builders booking through Cabin, it's a regulation that no longer applies to them.

This article summarises the April 2026 CIS reforms for general guidance. It isn't tax advice and shouldn't be relied on in place of professional counsel. If your situation is complex — directors' liability, large supply chains, existing HMRC disputes — speak to a qualified adviser. Primary sources: HMRC guidance on CIS reforms effective 6 April 2026, Autumn Budget 2025.