Boris: Design an electric family car and I'll buy it

The Mayor said that the electric car market needed the encouragement of consumer demand and promised never to buy another petrol-powered car.

But he said people needed a larger alternative to small electric cars such as the Toyota Prius to encourage them to ditch 4X4s.

Mr Johnson said: "It strikes me that after years of false starts, the electric market is on the verge of triumphant maturity, and all it needs is the encouragement of consumer demand.

"So here is my proposal to the motor industry, now languishing in the credit crunch. My Toyota people mover is so old and tired that if it were a dog, you would have it put down.

"But I intend to keep it on the road for another year, for two years, for three years - however long it takes the car manufacturers to produce a zero emission electric family car.

"I don't want to buy another internal combustion engine. There is a market waiting to be satisfied, and if that isn't an economic stimulus, I don't know what is." Mr Johnson's call came as Transport for London unveiled a range of new single- and double-decker eco-friendly hybrid buses, the first stage in an expansion of the city's hybrid bus fleet.

By the end of January next year, the number of hybrid buses in the London will more than quadruple to 56. A further 300 will be in operation by 2011.

Twenty-five hybrids will go into service this month on routes 16, 141, 276, 328 and E8; a further 18 will join the fleet early next year. Mr Johnson said: "A wonderful alliance of fuel efficiency and fume deficiency make hybrid engines the way to go for buses in our city.

"Londoners who travel on buses with the green leaf livery can rest comfortably in their seats and enjoy clear environmental consciences; safe in the knowledge that their journey will guzzle far less fuel and expire a whopping forty per cent less carbon dioxide than a regular bus."

Hybrid buses are cleaner and greener than their diesel counterparts. Their combination of a conventional engine and an electric motor uses less fuel and emits fewer pollutants - including 40 per cent fewer CO2 emissions.

Their roll-out will contribute to the Mayor's target of a 60 per cent reduction in emissions across London by 2025. Hybrid buses are also significantly quieter than diesel buses, making bus travel more pleasant for passengers and reducing noise for local residents who live along bus routes.

Alexander Dennis, Volvo and Optare have now produced their first hybrid buses for London, while Wrightbus has produced a new double deck hybrid, using different technology to that used in the 13 hybrids it already has operating in the London fleet.