As a barometer of the economy and in the minds of the public, few figures loom as large as the price of petrol. With prices at the pump rising 50 per cent in just over two years, drivers are feeling the pinch every time they fill up their tank; and for firms whose employees spend a lot of time on the road, the cost is being passed straight on to the business.

Both at individual and corporate level, you would imagine there had never been a better time to promote the green agenda, and encourage drivers off the roads. Yet while overall sales of petrol are 20 per cent down overall in the past year, according to International Energy Agency figures, business sales and mileage remain stubbornly static.