On 20 January 2023, the Foreign Secretary announced that the UK will play a leading role in a core group of likeminded partners to pursue criminal accountability for Russia’s illegal invasion of Ukraine. Alongside other international partners invited by Ukraine, the UK will shape thinking on how to ensure criminal accountability for Russia’s aggression against Ukraine. An investigation into the Crime of Aggression by any new tribunal could complement established mechanisms investigating war crimes, including the International Criminal Court and Ukraine’s domestic investigations and prosecutions. In joining this additional core group focused on Crimes of Aggression, the UK will complement its support on those other mechanisms in pursuit of accountability for war crimes, crimes against humanity, or genocide. Investigations for those international crimes are well underway, supported by UK initiatives such as the UK-US-EU Atrocity Crimes Advisory Group, and judicial training by Sir Howard Morrison KC and Uk-based Advocates for International Development. On 4 March 2023, it was announced that an International Centre for the Prosecution of Crimes of Aggression against Ukraine will be established in The Hague, within the structure of Eurojust’s Joint Investigation Team for Ukraine.