The library
Resources
Guides, analysis, and reference material on the April 2026 CIS regime, the "knew or should have known" standard, and what the evidence trail looks like in practice. Built for procurement directors, finance directors, accountants, and the advisers who support them.
Section 01 / Guides
Start here if you are new to the regime.
CIS Changes 2026: What Changed, and Who It Catches
A comprehensive guide to the new CIS fraud measures, what they mean for principal contractors, and how to prepare. The starting point if you are new to the new regime.
What CIS Verification Actually Checks (and What It Doesn't)
What HMRC's CIS verification covers, what it doesn't, and why the new regime requires both.
Section 02 / Reference
The essentials, kept current.
FAQ
Plain-English answers to the questions contractors are asking: the April 2026 changes, reasonable care, Gross Payment Status, director liability, subcontractor verification, and how Tax Radar fits in.
Go to the FAQ 41 TERMSGlossary
Every technical term used in the new regime, defined in working English, across CIS, case law, supply chain risk indicators, and the Tax Radar methodology.
Go to the Glossary PRIMARY SOURCESCompliance References
Primary legislation, HMRC guidance, and the case law construction will be judged against. The original sources behind the rules, gathered in one place.
Go to the ReferencesSection 03 / Articles
Analysis: how the regime got here, and how it is enforced.
Why HMRC's Fraud Investigation Service Is Targeting Construction
Construction has been a strategic enforcement priority. The April 2026 reforms are the next step in a fifteen-year arc, not a one-off legislative event.
The Kittel Countdown: Six Cases That Built the Test Construction Will Be Judged Against
The "knew or should have known" standard now in CIS is a VAT principle with nearly twenty years of UK case law behind it. These six cases tell contractors what HMRC will do next.
Joint and Several Liability in CIS: How HMRC's 20-Year Strategy Reached Construction
HMRC has been extending joint and several liability across the tax code for two decades. From 6 April 2026, construction contractors are formally in scope under sections 62A and 62B of the Finance Act 2004.
Behind the Curtain: The Anatomy of a Brown Envelope
A former HMRC Fraud Investigation Service operational lead runs the film backwards on a single enquiry letter: the sign-off, the intelligence package, and the year of work that happened before anyone knew it was happening.
When "I Didn't Know" Is Not Enough
How HMRC tests reasonable care, and how contractors lose. The George Star Builders ruling explained.
How We Score CIS Subcontractor Risk: A Methodology Note
Why anomaly detection outperforms checklist-based CIS due diligence, and what "reasonable care" looks like under the new regime in software terms.
Section 04 / In the press
Coverage and commentary.
CIS Joint Liability: What the New Legislation Means for Principal Contractors
Dan Lusted, co-founder of Tax Radar, on what a section 62A determination actually costs, what an HMRC enquiry gathers, and the due diligence record that answers it. In Scotland's construction news magazine.
Five Months Into the New CIS Fraud Regime, Silence Does Not Mean Safety
Dan Lusted, co-founder of Tax Radar, on why the absence of reported cases is not reassurance, and what reasonable care looks like five months into the new regime. In the magazine of the Chartered Institute of Building.
What the April 2026 CIS Changes Mean for Tax Advisors
Jack Sloggett, co-founder of Tax Radar, breaks down the April 2026 changes for tax advisers and their clients, in the monthly journal of the Chartered Institute of Taxation.
HMRC Broadens CIS Fraud Powers Beyond Direct Offenders
Coverage of the new legislation, featuring the analysis of Jack Sloggett, co-founder of Tax Radar, on the "knew or should have known" test and liability for fraud elsewhere in the chain.
New CIS Fraud Rules from April 2026: What Contractors Need to Know
Jack Sloggett, co-founder of Tax Radar, on what the test means in practice, how the new Gross Payment Status powers work, and the practical steps contractors can take now.
See what your supply chain looks like under CIS Defence.
The most useful conversation we have is not the one where we describe the new regime. It is the one where we put your actual supply chain in front of you, as CIS Defence sees it, and show you how your current position would survive contact with HMRC.