As with humans, corporate love triangles can become unstable and bitter. Germany's Volkswagen owns 30 per cent of compatriot truckmaker MAN as well as 36 per cent of the voting shares of Sweden's Scania. In return, Scania owns 14 per cent of MAN. The first spat occurred last year when MAN launched a hostile takeover of Scania. The Wallenberg family, which also controls a large stake in Scania, rejected the offer, and the deal finally collapsed because MAN refused some of VW's demands.

Since then, the share prices of MAN and Scania have soared on a combination of strong earnings and bid speculation of every permutation. Yesterday, reports emerged that Scania was considering a takeover of MAN. There are two reasons the stocks react to any sniff of corporate activity. First, there is compelling industrial logic for a tie-up that would create the world's third-biggest truck maker behind Daimler and Volvo. Second, investors are betting that VW, through its holdings in both MAN and Scania, is in the driving seat, and will ultimately make something happen.