WestLB, the German regional bank, threw markets into confusion on Thursday when it suddenly disclosed it had become the biggest shareholder in DaimlerChrysler, one of the world’s biggest carmakers.

The bank’s abrupt disclosure of a 14 per cent stake worth €9bn ($12bn) drew further attention to its trading activities as investors wondered whether it was a front for a new shareholder and if its move could affect Daimler’s possible sale of the lossmaking Chrysler division.