Russia, like the UK, is a member of the Council of Europe, which oversees the ECHR. To date the court has never awarded punitive or exemplary damages. It is being urged to do so in the exceptional circumstances of this claim and to prevent Russia from continuing its policy of covert elimination.

The legal arguments, submitted by Ben Emmerson QC, who represents Marina Litvinenko, refashion a claim first sent to Strasbourg in 2007 by her then lawyers, one of whom was Keir Starmer QC, now leader of the Labour party.

The UK government is cooperating with the Strasbourg court as it gathers evidence to assess the case. However, it has declined to intervene directly in support of the widow’s claim, partially on the grounds that it could affect the way the court deals with future British cases.

Alexander Litvinenko was a former KGB officer who spoke out about corruption inside Russia before fleeing with his family to Britain. He was poisoned with the radioactive isotope polonium-210.

The inquiry found it had been administered by two Russian agents, Andrei Lugovoi and Dmitry Kovtun, whom Litvinenko met in London. They have repeatedly denied involvement.