Among green-minded drivers in the urban centres and academic groves of Europe and America, hybrid cars - Toyota's Prius in particular - are the environmentally correct wheels of choice.

Mayor Ken Livingstone invites the cars into central London free of the city's congestion charge. California's governor, Arnold Schwarz-enegger, gives hybrids with good mileage ratings carte blanche in the state's car-pool lanes, even with only one passenger.