Inside the gleaming Moscow headquarters of TNK-BP, foreign managers of BP's Russian oil venture are under siege. Few speak now-adays on their mobile phones because they fear they have been bugged. Senior managers try not to discuss sensitive issues in their offices. One person there says he keeps a stack of paper and a whiteboard for scribbling down key words.

The future of the 50:50 venture created by the British group and a group of Russian billionaire shareholders in 2003 is in the balance amid a mounting battle for control. The outcome is likely to shape perceptions of President Dmitry Medvedev's new administration and the role foreign companies will be permitted to retain in the Russian oil sector as the state tightens its grip.