The use of secret evidence in terrorism trials has sustained significant academic critique in recent years, particularly in relation to special advocates in UK civil terrorism proceedings. Overlooked has been the use by courts of material from the reports of the UK's Independent Reviewer of Terrorism Legislation, an office established to review anti-terrorism laws. The Independent Reviewer may see classified material from intelligence and security agencies if necessary to carry out those reviews. The office thus has unprecedented access to material that is typically unavailable to courts. The conclusions drawn by the Independent Reviewer from this material have been adduced in legal proceedings in the UK and at the ECtHR. This paper documents how, when, why, and by whom material produced by the Independent Reviewer is used, both in UK courts and at the ECtHR. The purpose is to highlight an under-researched area of academic inquiry into the use of secret evidence in terrorism trials.