CIS Investigations: How HMRC's AI-Driven Compliance Strategy Is Changing Contractor Risk

If your business pays subcontractors for construction work, a CIS investigation is no longer something to think about only after HM Revenue & Customs (HMRC) gets in touch.

Under the Construction Industry Scheme (CIS), contractors are legally responsible for verifying subcontractors, applying the correct CIS deductions, submitting monthly returns and maintaining accurate records. These obligations have remained largely unchanged for many years.

What has changed is how HMRC identifies businesses for review.

According to HMRC's Annual Report and Accounts 2025 to 2026, the department generated £50.2 billion through compliance activity during the year, with around £10 billion supported through AI and advanced analytics. Alongside this continued investment in compliance capability, the Government introduced strengthened Construction Industry Scheme fraud measures in April 2026, giving HMRC greater powers to tackle abuse within labour supply chains.

For contractors, the message is clear. CIS compliance is no longer just about submitting monthly returns correctly. Businesses must also be able to demonstrate that every subcontractor has been verified correctly, deductions have been calculated accurately and appropriate records exist to support every decision if HMRC opens a compliance check.

This matters because subcontractor management sits at the heart of the construction industry. Contractwise's nationwide survey found that 88.9% of construction businesses engage subcontractors, yet only 35.8% believe they would be fully prepared if HMRC carried out a compliance audit tomorrow, highlighting a significant gap between confidence and investigation readiness.

What Is a CIS Investigation?

A CIS investigation is an HMRC compliance check into whether a contractor has met their obligations under the Construction Industry Scheme.

During an investigation, HMRC will review whether the contractor has applied the scheme correctly, maintained appropriate records and exercised reasonable care when managing subcontractors. Depending on the scope of the review, investigators may examine subcontractor verification records, CIS Returns, deduction calculations, contracts, payment records and supporting documentation to determine whether the contractor has complied with their legal responsibilities.

While many contractors associate investigations with suspected fraud or deliberate tax avoidance, this is not always the case. HMRC carries out compliance checks for a range of reasons, including verifying that businesses are operating the scheme correctly and identifying areas where additional tax may be due because of administrative errors or weaknesses in compliance processes.

The Construction Industry Scheme (CIS 340) guidance makes clear that contractors are responsible for verifying subcontractors, applying the correct deduction rates, submitting accurate monthly returns and retaining records that support those decisions.

For many businesses, a CIS investigation is therefore less about proving intent and more about proving process. Contractors that can clearly evidence how compliance decisions were made are generally in a much stronger position than those relying on fragmented records or manual administration.

Why HMRC's Approach to CIS Investigations Is Changing

The legal obligations placed on contractors under the Construction Industry Scheme have remained broadly consistent for many years. What is changing is the way HMRC identifies businesses that may require closer scrutiny.

Rather than relying solely on routine compliance activity or individual discrepancies, HMRC is increasingly investing in technology that enables it to analyse large volumes of tax data, identify patterns and prioritise cases where intervention is likely to have the greatest impact.

According to HMRC's Annual Report and Accounts 2025 to 2026, AI and advanced analytics supported around £10 billion of compliance yield during the year. At the same time, the Government has strengthened its approach to CIS fraud by introducing new powers to tackle abuse within labour supply chains.

For contractors, this represents a significant shift.

The question is no longer simply whether monthly CIS Returns are submitted correctly. Increasingly, businesses should expect to demonstrate that they have exercised reasonable care throughout the subcontractor lifecycle, from verification and onboarding through to payment, record keeping and due diligence.

This reflects a broader move towards evidence-based compliance. Contractors with consistent processes, complete audit trails and clearly documented decision making are likely to be in a much stronger position if HMRC requests information or opens a compliance check.

In practical terms, investigation readiness is becoming just as important as compliance itself.

What This Means for Construction Businesses: Rather than simply increasing the volume of investigations, HMRC's investment in AI and advanced analytics reflects a broader shift towards intelligence-led compliance. Contractors should expect businesses with stronger governance, clearer audit trails and more consistent processes to spend less time responding to enquiries, while those relying on fragmented records or manual administration may find compliance checks more disruptive.

In other words, good compliance is no longer just about meeting legal obligations. It's becoming an operational advantage.

What Can Trigger a CIS Investigation?

Many contractors assume a CIS investigation only follows deliberate tax avoidance or fraudulent activity. In reality, HMRC compliance checks often begin because a business's records or reporting indicate that further clarification is needed.

Issues such as incorrect subcontractor verification, inconsistent deduction rates, incomplete records or discrepancies between CIS, PAYE and VAT submissions may all increase the likelihood of HMRC making enquiries. On their own, these issues do not necessarily indicate wrongdoing. However, they can suggest weaknesses in the processes used to manage compliance.

The practical implication for contractors is that CIS compliance is increasingly being judged as a complete system rather than a collection of individual tasks.

Businesses should therefore think beyond submitting monthly returns. They should also consider whether they can readily demonstrate:

• How subcontractors were verified;
• Why a particular deduction rate was applied;
• What due diligence was completed before engagement; and
• Where supporting documentation is stored.

When those questions can be answered quickly and consistently, responding to an HMRC enquiry becomes significantly less disruptive.

Are Contractors Ready for a CIS Investigation?

While HMRC's ability to identify compliance risks is increasing, Contractwise's nationwide research suggests many construction businesses remain underprepared for an investigation.

Although 96.7% of contractors surveyed described themselves as confident in their CIS compliance, only 35.8% said they would be fully prepared if HMRC carried out a compliance audit tomorrow.

That gap is significant.

It suggests many businesses are successfully meeting their day-to-day compliance obligations but may struggle to retrieve evidence, demonstrate governance or explain historic decisions if HMRC requests supporting documentation.

The survey also found that 41.7% of respondents identified dealing with HMRC as the biggest challenge associated with CIS compliance, ahead of maintaining records, managing deductions or submitting monthly returns.

For contractors, the message is clear. Compliance is no longer measured solely by submitting returns accurately each month. Increasingly, it is about being able to demonstrate that every compliance decision can be evidenced quickly, consistently and with confidence.

As HMRC continues investing in data analytics and intelligence-led compliance activity, investigation readiness is becoming just as important as compliance itself.

Contractwise Insight: Modern CIS compliance is no longer measured solely by accuracy. Increasingly, it is measured by a contractor's ability to demonstrate that robust, repeatable processes were followed every time.

Five Practical Steps to Prepare for a CIS Investigation

Preparing for a CIS investigation doesn't require contractors to create new processes overnight. In most cases, it involves strengthening the procedures that should already exist and ensuring they are applied consistently across the business.

1. Build Verification Into Your Standard Onboarding Process: Many CIS compliance issues originate before work even begins. Verification should not be treated as an isolated administrative task but as a mandatory stage of every subcontractor onboarding process. Businesses that embed verification into a consistent workflow are less likely to encounter discrepancies later and are better able to evidence their decisions if HMRC requests information.
2. Treat Documentation as Evidence, Not Administration: One of the biggest challenges during any compliance check is retrieving historic information. Contracts, verification records, invoices and deduction calculations should not simply be retained to satisfy statutory requirements. They should be organised in a way that enables businesses to demonstrate how compliance decisions were made months or even years later.
3. Increase Visibility Across Your Labour Supply Chain: Recent changes to HMRC's approach reinforce the importance of understanding who is working within your supply chain and how subcontractors are engaged. Businesses should regularly review onboarding processes, carry out appropriate due diligence and ensure responsibilities are clearly documented. Greater visibility reduces both compliance risk and the likelihood of lengthy enquiries if HMRC requests further information.
4. Reduce Risk Through Consistency: Inconsistent processes often create inconsistent outcomes. Standardising subcontractor onboarding, verification, documentation and approval workflows helps reduce human error while making compliance easier to evidence across multiple projects, teams or locations.
5. Make Audit Readiness Part of Everyday Operations: Preparing for a CIS investigation should not begin when HMRC gets in touch. Businesses that centralise compliance records using a professional CIS payroll and auditing service, and maintain complete audit trails throughout the year are able to respond more quickly, minimise disruption and demonstrate confidence in their compliance processes.

Preparing for the Next Generation of CIS Compliance

The way HMRC investigates contractors is evolving.

While the core responsibilities under the Construction Industry Scheme remain unchanged, the department's increasing use of AI, advanced analytics and intelligence-led compliance activity means contractors should expect investigations to become more targeted and more evidence driven.

Businesses that continue to rely on manual processes, inconsistent documentation or fragmented subcontractor records may find it increasingly difficult to demonstrate compliance if HMRC opens an enquiry.

Contractwise helps contractors prepare for this changing compliance landscape by bringing subcontractor onboarding, verification, documentation and compliance records together in one place. By creating consistent processes and maintaining complete audit trails, businesses are better equipped to respond confidently, reduce administrative burden and demonstrate reasonable care throughout the subcontractor lifecycle.

Conclusion

HMRC is not simply increasing compliance activity; it is changing how compliance risks are identified and investigated.

As AI, advanced analytics and intelligence-led investigations become a larger part of HMRC's compliance strategy, contractors should expect greater emphasis on demonstrating robust governance rather than simply correcting isolated errors.

For construction businesses, this represents an opportunity as much as a challenge. Organisations that invest in consistent subcontractor onboarding, stronger audit trails and well-documented compliance processes are likely to spend less time responding to enquiries and more time focusing on delivery.

The question is no longer whether your business complies with the Construction Industry Scheme. It's whether you can demonstrate compliance with confidence, consistency and evidence whenever HMRC asks.

As compliance becomes increasingly intelligence-led, businesses that invest in stronger governance today will be far better prepared for tomorrow's investigations.