Thirty miles outside of Dushanbe, the dusty capital of Tajikistan, lies an aluminium smelter that will produce more than $1bn of the metal this year, the jewel in the industrial crown of a remote central Asian nation where six in 10 people live below the poverty line.

The company’s lawyers, by contrast, are more than 3,300 miles away in London, waging a legal battle over alleged profit-stripping that has quietly become one of the most expensive lawsuits contested in the English courts.