As leaders of the Group of Eight industrialised nations meet in St Petersburg on Saturday with energy high on the agenda, the spotlight is again turning on Dmytro Firtash.

Mr Firtash, a secretive Ukrainian businessman, has emerged as a key player in the European gas market at a time of heightened anxiety about security of supply. He disclosed this year that he was the co-owner, along with Russia’s Gazprom, of RosUkrEnergo, a joint venture that plays a central role in shipping gas from Russia and central Asia to Ukraine and the west.