When a crisis hits, the Council of Europe can be slow to act. But the Council responded promptly to Russia’s act of aggression against Ukraine, first by suspending Russia’s representation rights on 25 February 2022, and then, after 26 years of Russian membership, by expelling it on 16 March 2022, in accordance with Article 8 of its statute.

Now, the international prosecution of Russian leaders — which it is spearheading — cannot come soon enough, given the Kremlin’s intensified attacks against Ukraine’s civilian population.

On 8 July the world witnessed one of the worst days of violence against Ukrainian civilians in months. A barrage of missile strikes destroyed the main children’s hospital in Kyiv and pummelled cities across the country, killing at least 42 people and injuring more than 190. The number of children killed so far this year in indiscriminate attacks has increased by 40% compared to 2023, with more than 600 children having died since the start of the war.

Efforts are already underway to hold the Kremlin accountable for its actions. Last year, the International Criminal Court issued arrest warrants for Putin and Maria Lvova-Belova, Russia’s commissioner for children’s rights, for the unlawful deportation of Ukrainian children to Russia. Last month, ICC judges issued arrest warrants for former Defence Minister Sergei Shoigu and Chief of the Russian General Staff of the Armed Forces Valery Gerasimov for attacks on Ukraine’s electricity infrastructure.

Putin’s first and most blatant breach of international law, however, was planning and executing the invasion, occupation, and annexation of Ukraine. But despite having jurisdiction over war crimes, crimes against humanity (which now include the destruction of schools, hospitals, and infrastructure, and the deliberate targeting of civilians), and genocide committed on Ukraine’s territory, the ICC cannot prosecute Russian political and military leadership for the crime of aggression. That is because Russia is not a party to the Rome Statute, which established the court, and because the country’s veto power prevents the United Nations Security Council from referring the matter to the ICC.

A special international tribunal is thus required to prosecute Putin and his henchmen for this foundational crime. Of course, parallels will be drawn with other conflicts in the world, particularly in Gaza. But Putin’s deliberate and manifestly unlawful act of aggression started the current war in Ukraine, and his government’s planning of it — dating back to the invasion of Crimea in 2014 — makes it a clear-cut case for an indictment.

Opinion is divided, however, as to whether Putin can be held personally liable, given the debate over head-of-state immunity. Not surprisingly, Ukraine, as the victim of Putin’s aggression, and Russia’s neighbours, including Poland and the Baltic states, are of the view that Putin should be stripped of immunity.

But the United States, the United Kingdom, and France have so far favored maintaining immunity for heads of state, even before a wholly independent and international tribunal. They likely fear setting a precedent that could expose other leaders — perhaps even their own — to liability.

What we need is a common-sense test: no decent member of society whom I know believes that Putin should be granted immunity. Rather than remain a matter for diplomats and lawyers, such an important decision must reflect informed public opinion, which strongly disapproves of exempting Putin from prosecution.

One possible way forward would be to establish the tribunal without requiring an initial agreement on personal immunities, or with a flexible provision that is open to interpretation. The parties establishing the tribunal could, as the distinguished international legal expert Philippe Sands has suggested, decide that the issue of immunity will be governed by the applicable rules of international law. This, in effect, would allow the tribunal judges to decide on the matter.

We must urgently find a resolution to these concerns ahead of the US presidential election this November, as a second Donald Trump presidency could change the war’s trajectory and usher in a period of uncertainty. To end the impasse and establish the special tribunal on crimes of aggression in Ukraine, the UK’s new Labour government should invite the core group of stakeholders — the Council of Europe, Ukraine, and like-minded countries — to meet in London in September. This would enable the UK to signal its revulsion at Putin’s brutal war, as well as its willingness to lead the way in re-establishing the rule of international law.

The Council of Europe was founded in the aftermath of World War II, when huge swaths of Europe lay in ruins, with the goal of upholding the rule of law and human rights. Prosecuting Putin and his regime for the crime of aggression against Ukraine falls squarely within that mission. It would also send the important message that a rules-based, not a power-based, system is still the best way to create a more stable and peaceful world.