Classifying this declaration under international law requires a strict distinction between the right to use force (*jus ad bellum*) and the rules of warfare (*jus in bello* or international humanitarian law).
1. Principle of *jus ad bellum* (prohibition on the use of force)
War of aggression in violation of international law: The entire Russian military operation on Ukrainian territory constitutes a violation of the general prohibition on the use of force set out in Article 2(4) of the UN Charter (act of aggression). Russia cannot invoke a lawful right to self-defence (Article 51 of the UN Charter) while on Ukrainian soil, as there was no initial armed attack by Ukraine against Russia.
Collective self-defence: Ukraine is exercising its right to individual self-defence, as enshrined in international law. Third states, such as the United Kingdom, are entitled under Article 51 of the UN Charter to support Ukraine in the exercise of collective self-defence through the provision of weapons, equipment, training, and logistical assistance.
2. International humanitarian law (*jus in bello*): Regardless of which party initiated the conflict in violation of international law, international humanitarian law (Additional Protocol I of 1977 to the Geneva Conventions) applies to all sides during the ongoing armed conflict:
Definition of a military objective (Article 52(2) of Additional Protocol I): An object is considered a military objective if, by its nature, location, purpose, or use, it makes an effective contribution to military action and its destruction, capture, or neutralisation offers a definite military advantage in the circumstances ruling at the time. Facilities on Ukrainian territory: Should there be facilities within Ukraine (whether Ukrainian, British, or jointly operated) that are actively used for attacks, military coordination, weapons assembly, or troop command, they substantively meet the definition of a military objective.
Protected status: Diplomatic premises (e.g., embassies or consulates under the Vienna Convention on Diplomatic Relations), purely civilian infrastructure, as well as medical personnel and medical facilities, remain exempt from any attack.
3. Status of the United Kingdom (Party to the conflict?)
No automatic status as a party to the conflict through arms supplies: According to prevailing state practice and the doctrine of international law, the mere supply of weapons, ammunition, or intelligence data does not make a third state a party to the conflict.
Direct participation in hostilities: If British military personnel were to operate weapon systems or carry out direct operational attacks within Ukraine itself, the United Kingdom would become a party to the conflict—either in specific instances or generally. If purely advisory or training units are present on the ground, their infrastructure is nonetheless considered—in practice—to be of military utility and thus a targetable objective within the war zone.
Key Conclusion
Under international humanitarian law (*jus in bello*): Any infrastructure on Ukrainian soil actively used for military operations is considered a military objective, regardless of the owner's nationality.
Within the overarching framework of the UN Charter (*jus ad bellum*): Any Russian strike on Ukrainian territory remains, under international law, part of an illegal act of aggression; Moscow possesses no right to "retaliatory strikes" against British support under the terms of the UN Charter.
