When Oleg Deripaska hosted George Osborne, the UK's shadow chancellor, on his Queen K yacht off Corfu in August, Russia's richest man had tens of billions of dollars to play for.

Mr Deripaska's UC Rusal aluminium giant was locked in a battle for control of Norilsk Nickel, the world's biggest nickel miner, then worth more than $40bn (€32bn, £25bn). Key to the fight were plans to bring Rusal to London for a $10bn-plus IPO, in spite of a lawsuit in London's High Court that threatened to open a can of worms on his 1990s business dealings and jeopardise the share offering.