The use of armed drones by the United States, both within the conflict zones of Iraq and Syria, and further afield in Pakistan, Somalia, and Yemen, continues to be characterized by minimal public transparency, as the recent report, “Out of the Shadows,” released by Columbia Law School’s Human Rights Clinic and the Sana’a Center for Strategic Studies, makes clear. While a limited amount of information was finally disclosed at the very end of the Obama administration, the legal and policy rules governing the program remain opaque. Detail on individual strikes and casualty figures is lacking, internal CIA decision-making remains highly secretive, and the coverage of accountability procedures in place to respond to unlawful strikes is patchy at best.

The report is a salutary reminder that, despite the wide-ranging armed drone campaign having been in place for well over a decade, and having greatly grown in scope since the rise of ISIL/Daesh, fundamental questions remain as to how strikes are legally justified and how rigorous the U.S. government’s monitoring of these lethal activities really is.

But this lack of transparency regarding the legal and practical considerations underpinning the use of drones is hardly confined to the U.S. The United Kingdom’s participation in drone warfare, both through its own strikes carried out by the U.K.’s Royal Air Force (RAF) and through the U.K.’s involvement in the U.S. program, is also largely hidden from the public.

The U.K.’s approach to drone warfare is opaque at all levels of policy and practice. Officially, the U.K. has no formal drone program equivalent to that in the U.S. The U.K. Parliament’s Joint Committee on Human Rights inquiry into targeting killing concluded that, instead, armed drone strikes occur in an ad hoc manner as one of a suite of operational tactics at the disposal of U.K. forces. The U.K. government has, following freedom of information requests, released some figures indicating that by the end of 2016, more than 1,200 air strikes (both from conventional manned aircraft and drones) have been conducted by U.K. forces against ISIL targets in Iraq and Syria. Still, questions remain as to where else U.K. drones are deployed and the civilian impact of these strikes. While the data obtained through freedom of information requests is welcome, there is no regular official means through which the U.K. government informs the public of its participation in targeted strikes.

That is a troubling starting point, and it is indicative of the absence of transparency and scrutiny in this field. Leaving aside the figures, there is a concerning lack of clarity as to the legal basis upon which the U.K. relies for its use of armed drones, and, even more problematic, an apparent lack of willingness on the part of the U.K. government to provide clarity when requested.

One outstanding question is whether or not the U.K. is still asserting self-defense under international law for its use of drones. The government made such a claim after the RAF, in August 2015, killed three people, including the British citizens Reyaad Khan and Ruhul Amin, suspected ISIL operatives, in a drone strike near Raqqa in Syria. That strike took place despite Parliament having explicitly voted against U.K. involvement in U.S.-led airstrikes in Syria in August 2013 (a second vote in December 2015 subsequently approved such strikes). Then-Prime Minister, David Cameron, authorized the August strike without Parliament’s knowledge, and disclosed it only afterwards in September 2015. To do this, he relied on a limited Parliamentary convention, which allows for immediate military action to be taken in self-defense of British national interests without Parliamentary approval, so long as Parliament is provided with a full explanation as soon as possible afterwards. In providing the explanation, Cameron asserted that the strike was necessary because Khan represented a direct threat to Britain. Cameron specifically denied that the strike formed part of the US-led coalition’s military action in Syria. Confusingly, though, in the official legal notification to the United Nations Security Council, the U.K. claimed that the action was taken not only in self-defense of the U.K., but also pursuant to the right of collective self-defense of Iraq (that is, the inherent right under international law of all nations to act without U.N. Security Council approval to come to the defense of any nation subject to armed attack).

For a right of self-defense of the U.K.’s own interests to be engaged, in relation to the August 2015 strike, the use of anticipatory self-defense would need to be lawful. There is an ongoing controversy among international law experts as to the theoretical validity of the doctrine of anticipatory self-defense per se. The U.K. (together with the U.S., Israel, and a number of their allies) has long asserted the existence of such a right to anticipatory action. But even within the bounds of anticipatory self-defense, precisely how such a doctrine properly applies in the circumstances of strikes against ISIL targets overseas has never been adequately explained by the government. The U.K. Parliament’s Joint Committee on Human Rights and the Intelligence and Security Committee of Parliament have both sought clarification from the government as to its understanding of how the law applies to such strikes, and to the Khan strike in particular. Further, my organization Rights Watch (U.K.) requested disclosure, or a summary, of the relevant legal advice underpinning the action. The refusal of that request has been appealed and is before the Upper Tribunal (a U.K. administrative court) later this year.

But aside from a bland endorsement of the principles of the law of self-defense and an assertion as to all armed strikes’ compliance with the same, the U.K. government has been reluctant to clarify how the elements of the right to self-defense fit within the context of overseas drone strikes.

For example, the doctrine of anticipatory self-defense requires that the attack defended against must be an imminent one, but it is by no means clear what British authorities will judge as circumstances qualifying as imminent. That is troubling because 2017 has seen the U.K. Attorney-General, Jeremy Wright, in a speech to the International Institute for Strategic Studies, call for an approach to imminence, which eschews the traditional focus on the temporal proximity of the relevant threat in favor of a factor-based approach, in which the proximity of a threat in time is no longer a necessary condition. The Attorney-General favors action purportedly in self-defense even where the U.K. does not “know where and when an attack will take place, or the precise nature of the attack.”

Self-defense is a complex and contested subject within international law. But if the U.K. is approving drone strikes against non-proximate threats (say, threats that are at early stages of planning, rather than reaching a viable operational level) through a less stringent application of the imminence standard, that would be a significant departure in U.K. military practice. It is hard to see how it would be distinguished from the Bush doctrine of pre-emptive strikes overseas: a doctrine the U.K.’s Attorney-General during the Bush era, Lord Goldsmith, repeatedly repudiated.

The U.K.’s long-standing position (in line with the overwhelming majority of international opinion) has been to oppose the discredited theory of pre-emption. If the U.K. is to abandon its international legal posture – or indeed if the U.K. has already done so and is killing people overseas, including British citizens, by drone strikes in pursuit of a new legal theory – that fundamental change needs to be explained and subject to proper debate. Equally, if the U.K.’s drone program complies with orthodox international law, then the intelligence officers and members of the military who are carrying it out are due a clear and transparent explanation so as to remove the taint of illegality from their actions.

In addition to the absence of transparency and clarity with respect to the U.K.’s own use of drones, the U.K. government has also never set out the nature and degree of its involvement in facilitating and supporting the use of armed drones by the U.S. This is not merely a question of political and diplomatic interest, but a legal one also. For the U.K. may well, depending upon the nature of its involvement in the U.S. drone program, be liable as a matter of international law for the U.S. government’s actions.

Different rules of customary international law provide for accessory liability on slightly different bases. The International Law Commission’s Articles on the Responsibility of States for Internationally Wrongful Acts, which are generally taken to summarize the different bases of responsibility under international law, set out two separate ways in which one State may be held internationally responsible for the actions of another State it assists.

Article 16 provides that a State which “aids or assists another State” in the commission of any wrongful act is responsible if the assisting State “does so with knowledge of the circumstances of the internationally wrongful act” and the act “would be internationally wrongful if committed” by the assisting State. The International Court of Justice considered this type of liability in the Bosnia Genocide case, concluding that a State could be liable for aiding and assisting another to violate international law where it was actually aware of the plans of the other State prior to rendering assistance (a speculative opinion being insufficient).

Articles 40 and 41 provide a more narrowly focused rule, which applies only in circumstances where jus cogens norms of international law are concerned. Where one State is guilty of such a serious breach of international law, other States are prohibited from rendering any assistance whether beforehand or after the event in maintaining or recognizing the illegal situation. On notice of a serious breach of international law by a State, therefore, other States are obliged not to, for instance, provide further trade in arms or continue intelligence sharing.

Further, customary international law on the specific international crime of aggression – that is, the use of force outside the legal bounds of the United Nations Charter or the right to self-defense – provides that a State must not allow its own territory to be used as a launching pad for acts of aggression by other States. Such use of territory could include provision of landing rights for drone strikes, or even allowing partner State intelligence agencies to operate out of a State’s own military installations.

The U.K. cooperates closely with the U.S. drone program, and enjoys a high degree of knowledge as to the U.S. government’s conduct of it. Accordingly, it is entirely realistic that, insofar as the U.S. drone program may violate the norms of self-defense and/or international humanitarian law (by, for instance, failing to observe the distinction between civilian and military targets, or by causing disproportionate civilian harm), the U.K. may be liable under international law either for providing assistance before the fact, or for effectively sanctioning the U.S. government’s actions after the fact by continuing to provide intelligence and logistical support. While the U.K. government has acknowledged that the rules on aiding and assisting apply to the U.K., the government has never set out how it considers itself absolved from responsibility from assisting the much criticized U.S. drone program.

This lack of analysis is concerning, but is not unexpected: Rights Watch (U.K.) was recently involved in litigation in the English High Court arguing that the U.K. government was obliged to consider the U.K.’s potential liability for aiding and assisting breaches of international law by the Saudi Arabia-led coalition in Yemen through its arms exports to Saudi Arabia. But the government, far from providing comfort that the U.K.’s international liability is being seriously interrogated, argued in response that the modes of liability for aiding and assisting the acts of Saudi Arabia were simply irrelevant to that case.

As drone use proliferates internationally, the need for transparency and oversight also increases. But the failure of the U.S. and U.K. governments to provide regular reliable information on their participation in drone warfare, or to explain how their actions (both as principal and accessory) conform with their legal obligations, means that we can have no confidence that either country is acting lawfully. That is plainly unacceptable.

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