CIS is one of HMRC’s most tightly monitored areas. Many businesses make avoidable mistakes that later result in investigations.

Common CIS Mistakes

• Incorrect subcontractor status
• Wrong deduction rates
• Poor record keeping
• Mixing labour/materials incorrectly
• Late monthly returns

What Good CIS Looks Like

• Proper verification
• Clean documentation
• Labour/materials splits
• Early CIS returns
• Monthly HMRC reconciliation

Harbour offers structured CIS support, audit trails, and end-to-end compliance confidence.