BP could have to pay back $400m (£202m) to its Russia venture, TNK-BP, after a minority shareholder filed a lawsuit to declare an employment contract between the two companies invalid, as pressure mounts on the UK’s biggest Russian investment.

TNK-BP said a minority shareholder lawsuit filed this month alleges payments made by TNK-BP to BP for the employment of more than 150 specialists seconded from BP were extra dividends not received by remaining shareholders.