Sumption is a noted historian, justice of the UK Supreme Court and lead barrister in Seven Network Limited v News Limited  FCA 1062 (aka the C7 case).
His lecture [PDF] begins -
“The laws”, wrote the French novelist Honoré de Balzac, “are spiders’ webs, laid out to catch to catch little insects, which the great insects pass through unscathed”. In the law’s bestiary, there are few greater insects than the state. There is a school of thought that holds that the state is not only the greatest insect but also the most poisonous one. For a number of years the conduct of foreign affairs has served as one of the great forensic battlegrounds between those who take that view and successive governments who, understandably, do not.
There are a number of reasons why this should have recently become an issue. In the first place, in the short life of the present century, foreign affairs have generated moral issues of passionate concern to a significant part of our population, far more than any comparable period since the Second World War. Nuclear weapons development, relations with autocracies with poor human rights records, and the use of armed force in Iraq are just three of the more obvious examples. We may not believe, with Machievalli, that no subterfuge is too gross to be deployed in the interest of the state. But the polar opposite is just as problematic. It is exceptionally difficult to operate a morally pure foreign policy. Relations between states necessarily involve a measure of compromise between different and sometimes opposing values, even when one is dealing with countries that are both democracies and allies. The response of western democracies to the threat of international terrorism has at times been characterised, particularly in the United States, by a degree of ruthlessness that raises major moral issues of its own and is hard to reconcile with either their legal traditions or ours. Secondly, the growing emphasis in English public law on transparency, combined with the wide scope of the English rules of disclosure in litigation and the diminishing role of public interest immunity has exposed the workings of government in an area of human activity which has for centuries depended on the confidentiality of communications and the secrecy of intelligence-gathering operations. In a recent case, a Divisional Court took the view that the press had a distinct interest in the question whether communications about intelligence between the American and British governments, which had been the subject of a PII certificate by the Foreign Secretary should be published. I doubt whether this would have occurred to an earlier generation of judges. Third, and partly because of these factors, the operations of government in the domain of foreign policy and intelligence-gathering, have aroused intense distrust and suspicion in the press, an important section of the public and, it is fair to say, of the judiciary. This distrust is not easy to dispel without compromising the confidentiality of communications with foreign governments and the secrecy that is bound to protect intelligence work if it is to be effective. Fourth, the background to all of these developments, has been the exponential growth of judicial review over the past thirty years, which has led many people to look to the courts to inject a higher morality into public decision-making, untrammelled by the impurities of the political process. Law is animated by a combination of abstract reasoning and moral value-judgment, a heady mixture which seems a great deal more attractive and more honourable than the messy compromises that are in practice required to maintain relations with foreign states. In England, the significance of this factor is greatly increased by the breadth of the English rules about standing in judicial review proceedings. Just about any one can apply for judicial review if he has either a personal or an institutional concern which the outcome. This approach necessarily exposes the courts to a great deal of litigation which is essentially politics by other means. It opens the government to challenge in the courts by pressure groups, often concerned with a single issue, which have no interest in the process of accommodation between opposing interests and values that is fundamental to the ability of nations to live in peace. Fifth, and arguably the most important single factor, the enactment into English law of the European Convention on Human Rights, has obliged the court to scrutinise foreign policy decisions impacting on domestic human rights, in a way that would not have been required before. I shall say more about this factor later in this lecture.
It is a matter of speculation, but I suspect that if Britain were still a world power, the interests of the state would receive a larger measure of respect from both the public and the courts, as they once did in England and still by and large do in the United States. The projection of national power, whether hard or soft, no longer strikes most people as a major public interest on a par with, say, the protection of human rights at home and abroad. It is not my function to either welcome or regret these changes. I simply note that they have occurred and command broad assent among most of the politically informed population. They are therefore inevitably part of the background against which judges have to decide the growing number of cases relating to English foreign policy which come before them.
Until recently, foreign policy was one area in which government did indeed pass unscathed through Balzac’s spider’s web. The same was broadly true of the attendant domains of defence and intelligence. Almost every governmental act in the field of foreign relations is an exercise by ministers of the prerogative powers of the Crown. At one time, it was thought that that fact alone made it immune from judicial scrutiny. In Council of Civil Service Unions v Minister for the Civil Service  AC 374, the House of Lords held that the mere fact that the legal authority for an act of government was the prerogative of the Crown did not make it immune from judicial review, but that the subject matter of some prerogative powers might have that effect. Three out of the five members of the Committee expressed the view that foreign affairs were not susceptible to judicial review. This, according to Lord Roskill, was because “their nature and subject-matter is such as not to be amenable to the judicial process. The courts are not the place wherein to determine whether a treaty should be concluded or the armed forces disposed in a particular manner” (at p. 398). This judicial instinct was not peculiar to England. It is a feature of the law of a number of continental jurisdictions with highly developed systems of public law, including the Netherlands and Italy. It exists in most common law countries, and in particular in the United States, where the rules about standing are much tighter than they are in England, and the relative immunity of the executive’s foreign policy decisions from judicial scrutiny is probably the most robust part of the political questions doctrine. As Justice Jackson said in the Supreme Court in the famous 1950 case of Johnson v. Eisentrager 339 US 763, 789, “it is not the function of the judiciary to entertain private litigation... which challenges the legality, the wisdom or the propriety of the Commander-in-Chief in sending our armed forces abroad or to any particular region.”
The English courts, in keeping with their traditional suspicion of large constitutional theories, have not been very good at explaining why the courts should be any more reticent in dealing with the Foreign Secretary’s decisions than those of, say, the Secretary of State for Work and Pensions. Two approaches can be discerned in the various judicial statements on the matter. One is based on the concept of non-justiciability, and the other on the constitutional division of powers. ...