The move comes ahead of a management board vote today at which one of the oligarchs, Viktor Vekselberg, will call for the head of TNK-BP’s chief executive Bob Dudley.

If the oligarchs lose, they have threatened a blizzard of legal action against the BP-appointed TNK-BP directors, claiming they have breached their duties in backing Dudley.

BP’s claim, lodged in the HIgh Court last week, alleges the oil giant is owed the money under the terms of an agreement struck when the joint venture was created in 2003.

The writ says BP has tried three times to settle the issue, starting more than 15 months ago.

The oligarchs plan to fight the claim, arguing the figure in the writ is inflated. BP and the oligarchs have been at war since late last year.