The most common CIS payroll mistakes often begin with incorrect worker information, poor verification or assumptions about how somebody should be paid.
Agencies need to establish whether a worker is genuinely self-employed, consider Supervision, Direction and Control (SDC), and verify each subcontractor with HMRC before applying a deduction. Automatically deducting 20%, using incorrect hours or rates, missing timesheets or failing to recognise a change in a worker’s status can all result in incorrect payments.
Agencies also need to maintain accurate records and complete the required monthly CIS reporting, including dealing correctly with months where no subcontractors have been paid.
The consequences can range from worker disputes and additional administration to HMRC penalties and compliance problems. From 6 April 2026, increased scrutiny of fraud within the CIS supply chain also makes consistent verification, due diligence and record-keeping particularly important.
Common Mistakes
CIS payroll mistakes are rarely limited to getting a calculation wrong. An error can leave a worker underpaid, create disputes, cause problems with HMRC and make it difficult for an agency to demonstrate that it has handled its responsibilities correctly.
For recruitment agencies managing a fast-moving construction workforce, getting the fundamentals right every time is essential.
Read more: What responsibilities does an agency have when paying CIS subcontractors?
Could any of these mistakes affect your payroll?
Tick anything that applies to your current CIS process.
This checklist is a practical guide based on the issues covered in this article. It is not a substitute for an individual CIS or employment-status assessment.
Failing to verify a subcontractor correctly
One of the most significant mistakes is failing to complete the HMRC verification process correctly.
Before a subcontractor is paid through CIS, the agency needs accurate information, including the worker’s name, National Insurance number and Unique Taxpayer Reference (UTR).
If those details are incorrect or do not match HMRC’s records, the worker may be subject to the higher 30% deduction rather than the standard 20% rate.
That immediately creates a practical problem. The worker receives less money than expected and is likely to want to know why.
At Centurion Payroll, verification is therefore an important part of getting somebody set up correctly before their payment is processed.
Assuming someone is self-employed because they say they are
Having a UTR does not automatically mean somebody should be paid through CIS.
Neither does the worker saying that they are self-employed or asking the agency to pay them that way.
The agency first needs to consider the reality of the working arrangement, including whether Supervision, Direction or Control (SDC) exists or there is a right for it to exist.
Where SDC applies, PAYE may be the appropriate payment route instead.
Getting this wrong is more significant than applying the wrong deduction percentage because the worker may have been put through the wrong payroll arrangement from the beginning.
Automatically deducting 20%
It can be easy to associate CIS with a 20% deduction, but agencies shouldn’t simply apply that percentage to every subcontractor.
HMRC verification determines the appropriate treatment.
Depending on the result, the subcontractor may be paid gross, have the standard 20% deduction applied or be subject to the higher 30% deduction.
That verification result needs to drive the payroll calculation rather than an assumption about what rate normally applies.
Not keeping on top of changes to a worker’s status
Verification shouldn’t be thought of as information that can simply be forgotten once it has been obtained.
A subcontractor’s circumstances or status can change.
One potential mistake is continuing to pay somebody gross when their status has changed. The payroll information being used therefore needs to reflect the worker’s current position.
This is another reason accurate verification records and a clear payroll trail matter.
Dave Davies, Managing Director of Centurion Payroll, explains:
“Most CIS payroll problems come down to getting one of the basics wrong. If the worker’s status, verification, timesheet or deduction isn’t right, you can quickly end up with an incorrect payment and an unhappy worker. The key is having a consistent process and accurate records from the start.”
Missing somebody because their timesheet isn’t on the schedule
Not every CIS payroll mistake starts with HMRC. Some begin with something as simple as a missing timesheet.
Construction recruitment agencies can be dealing with large, changing workforces spread across multiple sites. Workers join, leave and move between assignments, often quickly.
If a timesheet isn’t received, isn’t approved or doesn’t make it onto the payment schedule, the worker can be missed altogether.
From the worker’s perspective, the reason doesn’t change the outcome: they expected to be paid and haven’t been.
A clear process for collecting, approving and matching timesheets to the payroll schedule helps reduce that risk.
Using the wrong hours or rate
The worker can also be included in payroll but still receive the wrong amount.
Agencies need to provide accurate approved hours or days and the correct hourly or daily rate. Where a worker has different rates, these need to be clearly identified.
If ten hours are entered instead of twelve, or the wrong rate is selected, the CIS calculation could technically be correct while the final payment is still wrong.
That creates additional work for the agency and payroll team and, more importantly, can quickly undermine the worker’s confidence in the payment process.
Missing the monthly CIS return
The payroll process doesn’t end when money reaches the subcontractor.
The appropriate CIS reporting also needs to be completed with HMRC.
Failing to submit a required monthly CIS return can expose the agency to penalties, while inconsistent reporting can create discrepancies between the agency’s own records and the information supplied to HMRC.
This is why CIS needs to be managed as an ongoing compliance process rather than simply a weekly payment exercise.
Assuming a nil month means nothing needs to be done
From 6 April 2026, agencies also need to pay particular attention to months where no subcontractors have been paid.
A CIS-registered contractor with no subcontractor payments during a tax month may still need to submit a nil return or notify HMRC in advance that no payments will be made.
In other words, no payments doesn’t automatically mean nothing to report.
Agencies need a process for identifying these months rather than simply allowing them to pass because there was no CIS payroll to run.
Keeping incomplete or inconsistent records
Good records are an important part of CIS compliance.
An agency should be able to connect the worker’s verification and status with their timesheet, gross payment, CIS deduction, net payment and the information reported to HMRC.
Problems arise when those records don’t agree.
For example, if the payment records show one figure but a different amount was reported to HMRC, identifying what happened later can become unnecessarily difficult.
Workers also need accurate records showing their gross payment and deductions.
A clear paper trail isn’t simply useful administration. It helps demonstrate how and why a worker was paid in a particular way.
Ignoring unusual arrangements within the supply chain
Agencies also need to think beyond the individual payroll calculation.
There are changes taking effect from 6 April 2026 that increase the importance of identifying suspicious arrangements within the CIS supply chain.
Its guidance explains that HMRC will have stronger powers where a business knew, or should have known, that payments were connected with fraud.
Potential consequences include loss of Gross Payment Status, liability for lost tax, financial penalties and restrictions on reapplying for gross status.
That makes consistent verification, due diligence and record-keeping much more than an administrative exercise.
Small payroll mistakes can create much bigger problems
The immediate consequence of a CIS payroll error might be one worker questioning their payment, but the effects can go considerably further.
Incorrect deductions can damage trust with workers. Missing timesheets can result in missed payments. Incorrect hours or rates create queries and additional administration. Missing returns can result in HMRC penalties, while inadequate records can make it difficult to demonstrate that the correct process was followed.
And where there are unusual or potentially fraudulent arrangements within the labour supply chain, the consequences can become significantly more serious.
For agencies, the answer is consistency: assess status correctly, verify every subcontractor, use accurate payment information, apply the HMRC verification result, maintain clear records and complete the required reporting. To find out more about an agencies reposnasibility, read our blog.
At Centurion Payroll, our role is to take the payroll administration off the agency’s desk while helping make sure workers are paid accurately and on time, every time.
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