Over two astonishing days in October 2008 one of the most amazing stories of the downturn emerged. Porsche, the luxury sports car manufacturer, was revealed as the force behind an audacious takeover bid for Volkswagen.

The price of Volkswagen shares rocketed fivefold, and it briefly became the most valuable company on the planet. And hedge funds that had been betting on VW shares falling in the downturn found themselves staring at losses that ran into billions of pounds.

Now the German authorities are investigating. It has been alleged that the much smaller German car maker Porsche manipulated the market, made a fortune and ended up potentially taking over its rival.

Porsche insists it has done nothing wrong. But for years it has quietly stalked its larger rival, buying up VW shares in a creeping takeover and making vast profits in dealings on those shares. It has been highly effective, last year it made four times as much money from share trading than from making its iconic sports cars.

The Money Programme's Max Flint travels to Germany to investigate how Porsche became so expert in playing the market and how it could end up with the biggest prize of all: control of its rival.

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