[W]hy should acts of a foreign judiciary be treated differently from other acts of state, and what is the basis of that difference? – the answer, in our judgment, is that judicial acts are not acts of state for the purposes of the act of state doctrine. The doctrine in its classic statements has never referred to judicial acts of state, it has referred to legislative or executive (or governmental or official) acts of a foreign sovereign. [...]. It is not hard to understand why there should be a distinction. Sovereigns act on their own plane: they are responsible to their own peoples, but internationally they are responsible only in accordance with international law and internationally recognized norms. Courts, however, are always responsible for their acts, both domestically and internationally. Domestically they are responsible up to the level of their supreme court, and internationally they are responsible in the sense that their judgments are recognizable and enforceable in other nations only to the extent that they have observed what we would call substantive or natural justice, what in the United States is called due process, and what internationally is more and more being referred to as the rule of law. In other words the judicial acts of a foreign state are judged by judicial standards, including international standards regarding jurisdiction, in accordance with doctrines separate from the act of state doctrine, even if the dictates of comity still have an important role to play [...] ‘[O]nly the more normal restraints of judicial comity hold sway in that judicial context.’
Yukos Capital Sarl v OJSC Rosneft Oil Company [2012] EWCA Civ 855
