U.K. foreign secretary's remark on the use of British weapons does not give Russia the right to attack

Context 

During a visit to the Ukrainian capital, Kyiv, on May 2, 2024, British Foreign Secretary David Cameron said Ukraine could use UK-supplied weapons to strike targets inside Russia. 

"Ukraine has that right. Just as Russia is striking inside Ukraine, you can quite understand why Ukraine feels the need to make sure it's defending itself," the Foreign Secretary told Reuters. 

The remarks have spurred claims online that they "give Russia the right under international law to strike British Territory." 

But the claims are false, say experts in international law. Weapon deliveries do not make Britain a party in the conflict. It is Ukraine's responsibility to determine how the weapons are used.   

In fact

Frederik Harhoff, Professor Emeritus in international law at the University of Southern Denmark, told Logically Facts Cameron's remarks do not give Russia the right to strike British territory. 

"Liability can only be directed at the person using the weapon and the organisation they are a member of," he said. 

He asked us to consider a scenario where every country that produced and exported weapons or weapon components to Russia was to be held accountable for a Russian attack on Ukraine. "It would be illegal to produce weapons at all," he said. 

Tonny Brems Knudsen, an associate professor in political science at the University of Aarhus, Denmark, whose research includes using force in international law, agreed that Cameron's remarks couldn't legitimise Russian strikes on Britain. 

"Britain delivering weapons to Ukraine does not mean it participates in armed attacks against Russia. How far Ukraine chooses to go with those weapons and whether Ukraine stays within the rules of the right to self-defense is Ukraine's responsibility," he said, adding that under international law Ukraine has the right to defend itself against ongoing Russian attacks by striking bases, weapon production facilities and the like within Russia.

Cornelius Wiesener, a tenure-track assistant professor researching international law and military operations, calls it a common misconception that by delivering weapons, the U.K. - or any other country - would become party to the ongoing armed conflict between Russia and Ukraine and may this be targeted with impunity. He lists two reasons. 

"Firstly, just providing weapons as such is not enough to become party to the conflict. Usually, that would require boots on the ground, engaged in combat with Russian soldiers," he said. "Secondly, even if we assume the U.K. were to become a co-belligerent simply because of its arms delivery, any attack on the U.K. would still be illegal as it would be another illegal use of force - aggression - on Russia's part, for which it can be held responsible and asked to make reparations."

He offered the historic parallel of Nazi Germany invading Poland in September 1939, through illegal use of force, prompting France and the U.K. to declare war on Germany. "This did not give Germany the right to invade France and try to invade the U.K. Even though the (attempted) invasions as such were in line with the law of armed conflict and so weren't violations in the field of international law, they still amounted to illegal uses of force," said Wiesener. 

The U.K. could conceivably be held responsible for complicity in acts violating international law if it continued deliveries as Ukraine used the weapons to violate international law, for example, by going beyond what can be justified as self-defense, or to commit war crimes, said Jens Elo Rytter, a professor in international law at the University of Copenhagen.   

"However, this is a question of legal responsibility and would not in itself justify military retaliation from the Russian side," he said.

Russia's foreign ministry responded yesterday to Cameron's remarks, warning that "any British military facilities and equipment on the territory of Ukraine and abroad" could be targeted "in response to Ukrainian attacks on Russian territory with British weapons."

The verdict

Weapon deliveries do not make Britain party to the conflict. How Ukraine uses the weapons, how far it chooses to go and if it stays within the rules of the right to self-defense is Ukraine's responsibility. Therefore, we have marked this claim as false.