This article investigates UK judicial engagement with the war and related foreign affairs prerogatives, specifically considering developments in judicial review since 2002. It outlines the comparative strengthening of judicial checks on high policy prerogatives during this period, but finds that such advances have had minimal impact in real terms; case outcomes remain unaltered and prerogatives in this area are still afforded special treatment by the judiciary. The specific aim of this article is to identify underlying reasons why, despite appearances, there has been no actual material departure from the traditional GCHQ position which ring-fenced such prerogatives as immune from judicial scrutiny. To this end it conducts a detailed analysis of caselaw, identifying and discussing two interrelated reasons. First, in war and foreign affairs matters the judiciary employ boundaries between law and non-law, specifically eliminating political or policy issues from their concern. However, attempting to maintain the ‘internal purity’ of law involves judicial concessions in other respects; the way in which the courts apply boundaries is selective and inconsistent, ultimately acting to favour the government of the day. Second, knowledge or expertise is a key factor underlying judicial approaches in war, defence and foreign affairs. Executive views in this area have always enjoyed precedence in the courtroom and this is logically justified on the basis that government has superior expertise and exclusive access to information in this area. The precedence of executive views has continued in recent caselaw, undermining the appearance of strengthening judicial checks. The weight that courts afford government evidence in such areas is, for the most part, institutionally mandatory and it must therefore be concluded that the courts are incapable of effectively checking ministerial prerogative in war and related foreign affairs.