CIS | Contractors
CIS Subcontractor Verification 2026 - How to Verify, the 30% Trap, and Common Mistakes
Before you pay a subcontractor under the Construction Industry Scheme, HMRC requires you to verify them. The verification process tells you exactly how much CIS tax to deduct from their next payment, and getting it wrong can cost both sides real money. Verify too late and you have to deduct at 30 per cent rather than 20 per cent, which is a 10 percentage point cash flow penalty your subcontractor will absolutely notice. Verify too lazily and you have no documentation if HMRC asks why you deducted at a particular rate.
This guide explains the verification process, what the three possible results mean, why the 30 per cent unverified rate exists, and the common mistakes that quietly cost contractors money every month.
Why Verification Exists
CIS was designed to combat tax evasion in construction. Before the scheme, large numbers of construction workers operated cash-in-hand, declared little or no income, and HMRC lost substantial revenue. CIS forces tax to be collected at source from contractor to subcontractor, which means the tax has already left the system before the subcontractor has a chance to spend or hide it.
Verification is the gatekeeper. Before a contractor pays a subcontractor, they verify them with HMRC. The verification process confirms that the subcontractor is genuinely registered with HMRC for CIS, has a valid UTR, and is known to the system. The verification result tells the contractor exactly what rate to deduct at, which then gets reported on the monthly CIS300 return.
Without verification, contractors would have no way to know whether a subcontractor turning up on site with a "I'm CIS-registered" claim was telling the truth.
The Three Possible Verification Results
When you verify a subcontractor with HMRC, one of three things comes back:
Result 1: Gross Payment Status (0% deduction)
The subcontractor has Gross Payment Status, meaning they have passed HMRC's three-test process (business, turnover, and compliance). You pay them the full gross invoice amount with no CIS deduction at all. They settle their tax through Self-Assessment at year-end. HMRC provides a verification number that goes on your CIS300 return.
Result 2: Standard Verification (20% deduction)
This is the most common result. The subcontractor is properly registered for CIS but does not have gross payment status. You deduct 20 per cent from the labour portion of their invoice (excluding VAT and materials) and pay it to HMRC. They will reclaim most of it back through their Self-Assessment refund. HMRC provides a verification number.
Result 3: Unmatched / Unverified (30% deduction)
HMRC cannot match the subcontractor's details against their CIS records. This usually means the subcontractor has not registered for CIS at all, or has given you incorrect details (wrong UTR, wrong NI number, name typo). You must deduct at 30 per cent rather than 20 per cent until they sort their registration out and you re-verify. There is no verification number to record because HMRC could not verify them.
The 30 per cent rate is deliberately punitive. HMRC wants subcontractors to register properly for CIS, and the easiest way to make that happen is to make unregistered work expensive. A subcontractor losing 10 percentage points of cash flow to unregistration usually fixes their position quickly.
How to Verify a Subcontractor
You verify subcontractors through HMRC's CIS online service, by phone to the CIS helpline (0300 200 3210), or through CIS-compliant bookkeeping software (Xero, QuickBooks, Sage and similar all do this directly).
For each subcontractor, you need:
- For individual subcontractors: their name, UTR (Unique Taxpayer Reference, 10 digits), and National Insurance number.
- For partnerships: the partnership name, partnership UTR, and the UTR of at least one partner.
- For companies: the company name, company UTR, and Companies House registration number.
HMRC returns the verification result almost immediately and provides a verification reference number for any standard or gross verification (no reference number is provided for unmatched results). You record this reference number against the subcontractor in your records, and it goes on every monthly CIS300 return that includes payments to them.
The 30% Trap and How to Avoid It
The most common compliance failure we see is contractors paying unverified subcontractors at 20 per cent rather than 30 per cent. This happens for several reasons:
- Verification not done before payment. The contractor pays the subcontractor in the rush of a busy week and intends to verify "later". Later turns into a few days, then a few weeks, and when verification finally happens the subcontractor comes back as unmatched. The 20 per cent already deducted was wrong; it should have been 30 per cent.
- Assuming previous verification still applies. Verification status is not permanent. HMRC can revoke gross payment status. A subcontractor's registration can lapse. We see contractors using a verification from 18 months ago that is no longer current.
- Subcontractor gives wrong details. The UTR has a digit transposed, the NI number has a letter wrong, the name on the bank statement does not match HMRC's records. Verification fails and the contractor either re-verifies (correct) or pays anyway at 20 per cent (incorrect).
- Verification done but not recorded properly. The contractor verifies but does not capture the verification reference number, so when HMRC audits the CIS300 returns there is no audit trail.
The consequences of getting the deduction rate wrong fall on the contractor, not the subcontractor. HMRC will pursue the contractor for the under-deducted tax (the 10 percentage point difference between 20 and 30) plus interest plus penalties. The subcontractor's position is fine because they reclaim through Self-Assessment anyway, but the contractor is left with an unexpected tax bill.
How Long Does Verification Stay Valid?
HMRC's rule is that you can rely on a verification for up to two years from the date of the most recent payment, provided you have actually paid the subcontractor at least once in the previous two CIS tax years.
If you stop using a subcontractor for two CIS tax years and then start paying them again, you must re-verify. Even within the two-year window, HMRC encourages contractors to re-verify periodically because subcontractor status can change (gross status can be withdrawn, registrations can lapse).
Most reputable contractors re-verify subcontractors at the start of each tax year as a matter of routine. It takes minutes per subcontractor and removes any doubt.
Real-Life Example
Wembley contractor: £3,800 HMRC assessment over verification failures
Client S ran an electrical contracting business in Wembley, engaging four or five subcontractor electricians at any time on commercial fit-out and residential projects. His previous accountant had been filing CIS300 returns each month but the underlying verification process was loose. He typically paid subcontractors first and verified later when he remembered.
One of his subcontractors, who had worked with him for three years, had quietly let his CIS registration lapse during a year when he had taken on PAYE employment elsewhere. When he came back to subcontracting work for Client S, he was paid at the standard 20 per cent rate for four months before anyone re-verified. The re-verification, when finally done, returned an unmatched result. Client S should have been deducting at 30 per cent throughout those four months.
HMRC picked it up during a routine CIS compliance review. The under-deducted tax across the four months came to around £2,400. Add interest and penalties, the total assessment was around £3,800. The subcontractor's tax position was unaffected (he reclaimed through his own Self-Assessment as normal) but Client S was personally liable for the contractor-side shortfall.
We put a verification process in place: every subcontractor verified at the start of each tax year, every new subcontractor verified before the first payment, and the verification reference number recorded in Xero against each subcontractor's contact record. The £3,800 assessment was avoidable noise; the discipline going forward is now properly embedded.
Common Verification Mistakes to Avoid
Patterns we see repeatedly with new contractor clients:
- Verifying after payment rather than before. The whole point of verification is to know the right rate before you pay. Paying first and verifying after creates the exact problem the scheme is designed to prevent.
- Trusting the subcontractor's claim about their own status. A subcontractor saying "I have gross payment status" is not enough. HMRC verification is the only proof that counts. Verify directly.
- Using out-of-date verifications for long-running relationships. Re-verify annually as a minimum, even for trusted subcontractors you have used for years.
- Not recording the verification reference number. The reference number is the audit trail. Without it, HMRC has no way to confirm you actually verified.
- Letting the office bookkeeper or site manager handle verification informally. This is a tax-critical process. One person needs to own it (usually whoever owns the monthly CIS300 return) and the process needs to be documented.
- Not verifying nil-payment situations. If you have engaged a subcontractor but are about to pay them for the first time, verify even if the first payment is small. The first payment is when verification matters most.
Frequently Asked Questions
Frequently Asked Questions
How long does it take to verify a subcontractor?
Online verification through HMRC's CIS service or through bookkeeping software is usually instant. The verification result and reference number come back within seconds. Phone verification through the HMRC helpline takes longer due to call queue times but is otherwise straightforward.
What happens if a subcontractor refuses to give me their UTR?
You cannot properly verify them and must therefore deduct at 30 per cent rather than 20 per cent. Most subcontractors quickly hand over their UTR once they understand the 10 percentage point cash flow cost of not doing so. A subcontractor refusing UTR information is also a sign that something is wrong with their tax position, which is worth knowing.
Can I verify subcontractors retrospectively to fix old returns?
You can verify retrospectively for the current period, but you cannot fix historical wrong deductions just by verifying now. If you have under-deducted in past months, you need to amend the relevant CIS300 returns and pay the additional tax. We routinely help contractors clean up historic verification issues.
If a subcontractor has gross payment status, do I still need to verify them?
Yes. Verification is what confirms their gross status to you in the first place. Without verification, you have no proof that they have gross status and cannot pay them at 0 per cent CIS deduction.
What records do I need to keep around verification?
The verification reference number returned by HMRC, the date of verification, the subcontractor's details (name, UTR, NI or company number) used in the verification, and the deduction rate applied as a result. Most bookkeeping software stores all of this against the subcontractor's contact record automatically.
Need help getting your CIS verification process right?
At Your Tax Help Accountants in Stanmore, we handle CIS verification, monthly CIS300 returns and the full contractor obligation for clients across Harrow, Wembley, Edgware and London. Fixed monthly fees, no surprises, every subcontractor properly verified before payment.
Or email info@yourtaxhelp.co.uk | yourtaxhelp.co.uk
General guidance only. Not personal tax advice. Contact us for advice specific to your situation. All figures are for the 2026/27 tax year unless otherwise stated.