Petrol and diesel prices are high, congestion charges and road taxes are mounting, and many people are starting to feel a gnawing guilt over belching more carbon dioxide into the atmosphere. All in all, the market for electric cars, with "green" credentials, could not be better.

A growing number of electric vehicles are visible on today's roads. But a wholesale defection from conventional internal combustion engines is being stalled by two currently insurmountable obstacles.