Investigators at Russia's interior ministry questioned the BP-backed chief executive of TNK-BP for almost six hours on Tuesday as the struggle deepened between BP and its Russian partners for control of the oil venture.

Robert Dudley was questioned as a witness in a probe into tax evasion at TNK between 2001 and 2003, TNK-BP said. The investigation related to TNK’s activities before it was merged with BP’s Russia assets in 2003 and before Mr Dudley became chief executive, TNK-BP said.