An unusual arbitration case relating to a dispute over a 19th-century land deal has pitted the government of Malaysia and two leading independent European firms against one of the world’s largest litigation funders, as the debate over whether to regulate third-party litigation funding in the EU intensifies.

The case centres on a 2018 claim by a group of Filipino citizens, who say they are the descendants of the last Sultan of Sulu, regarding compensation they say they are owed by Malaysia for their ancestors’ former land in the oil-rich state of Sabah under a 1878 forever lease agreement. The claimants are being backed by Therium, among the biggest litigation funders.