The UK Investigatory Powers Tribunal, the court responsible for determining human rights claims with regards to state surveillance, has developed procedure which serves to reduce the reliance on secret evidence in a case. Rather than establishing security-sensitive facts regarding the UK’s surveillance regime in closed proceedings, the procedure involves assuming certain facts regarding the nature of the surveillance regime to be true. The Tribunal then usually rules on the legality of the regime – on the basis of assumed facts – in open proceedings, while primarily only using closed sessions to assess specific instances of surveillance. The paper assesses this form of procedure and the impact it has on accountability. It is argued that while it may help to promote greater openness surrounding the judicial process in surveillance cases, it brings with its own limitations from the perspective of holding the Government to account with regards to its surveillance practices.