Cousins in control: Wolfgang Porsche (left) in a 2009 Panamera and, a decade earlier, Ferdinand Piëch in a Bugatti EB218. The global crisis is intensifying a family feud

In any list of career mistakes, a letter written by Arno Bohn 17 years ago would rank highly. As chief executive of Porsche, he wrote to Ferdinand Piëch to suggest the grandson of the founder of the German sports carmaker should resign from the supervisory board of the company, then on the brink of bankruptcy.