When Vladimir Potanin announced that he was splitting from Mikhail Prokhorov, his business partner of 16 years, he never thought it was going to be easy. But he did not expect it to be quite as hard as it is proving to be.

Ever since proposing the split in January, Mr Potanin, who chairs Norilsk Nickel, has been in a deadlock with his erstwhile partner over how to split the two billionaires' holdings in the mining company.