Is The UK Now A Co-Combatant In Ukraine?

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The day after Russia invaded Ukraine, as Kiev's allies scrambled to find a response, it was reported that the US government was reviewing the legality of providing arms to help with the country's defense.

Within days, Russia's president, Vladimir Putin, had declared that even imposing economic sanctions would be an“act of war.” His defense ministry released a statement that if third-party countries allowed Ukraine to use their bases as a safe haven for Ukrainian aircraft, then“subsequent use against the Russian armed forces can be regarded as the involvement of these states in an armed conflict.”

Since the Second World War, the laws of neutrality have been interpreted so that states can provide weapons and other support to a state unjustly attacked by a belligerent country, to enable it to defend itself. According to this definition, third-party countries would become co-combatants only if they resort to armed force against Russia.

Russia's incursion into Ukraine has been ruled as a flagrant breach of Article 2(4) of the UN Charter , which prohibits the“use of force against the territorial integrity or political independence of any state.” Russia's war in Ukraine has been denounced as an act of aggression by the UN General Assembly and the International Court of Justice .

Moreover, it is claimed that Russia has been implicated in breaches of international humanitarian law through its apparent indiscriminate bombing and other violent attacks, and crimes against civilians . This would mean that anyone supplying Russia – the belligerent in this conflict – with arms is in breach of international law.

But the question remains, if it is legal to supply Ukraine with weapons to help defend itself, would actually helping the Ukrainian military use them to hit Russian targets make the UK a co-combatant?

While the law is not settled, legal scholars believe supplying Ukraine with the means to defend itself against Russia does not in itself constitute a breach of international law – and nor does it make the UK a co-combatant.

Any action by UK forces would only constitute a combat operation if these actions, carried out by UK personnel without any further action by Ukrainians, would launch a missile or any other kind of attack on Russian forces.

Risk of escalation

But there remains the question of escalation. Whatever the legal situation – and Russia has shown itself willing to ignore the rules of warfare by violating Ukraine's territorial integrity since the incursions of 2014 and in the full-scale invasion in February 2022 – Putin and his senior ministers have regularly warned Kiev's Western allies that their aid may constitute an escalation to which it would respond with all available means, including nuclear weapons.