Testing Porsche's new 2010 Hybrid Cayenne prototype

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We're doing about 35mph, and the road suddenly turns straight and empty enough for Dr Michael Leiters to sink the Cayenne's accelerator. Not all the way to the floor but firmly enough to feel the Porsche surge forward in a smooth stream of unhesitating power.

Nothing remarkable about that, you may think, except that this Cayenne has switched from pure electric propulsion to a petrol-electric combination, and all without the slightest shudder, tremor or shake. What happened, when Porsche development engineer Leiters accelerated, was complex and perfectly synchronised. The electric motor continued spinning, and was joined in an instant by a petrol engine that had previously been turned off. An electronically controlled clutch, operating with incredible precision, allowed one engine to spin up to the speed of the other without causing clunks or jerks. Admittedly this is a Porsche engineer driving this car rather than your reporter, but we go far enough and hard enough to make it pretty unlikely that he is covering things up.