Switching to electric vehicles will not on its own have a significant impact on Britain's carbon emissions, a report said yesterday.
Success depended on the availability of "green" electricity and overcoming a number of major technical problems, said the Royal Academy of Engineering.
Roger Kemp, from Lancaster University, who chaired the Academy's Electric Vehicles working group, said: "Swapping gas guzzlers for electric vehicles will not solve our carbon emissions problem on its own.
"When most electricity in Britain is still generated by burning gas and coal, the difference between an electric car and a small, low-emission petrol or diesel car is negligible.
"We welcome the fact that the motor manufacturers are so ready to take on the challenge of developing mass market electric vehicles. We also welcome the new government's commitment to mandating charging sockets for electric vehicles and plug-in hybrids, but establishing these as the technology of choice for personal transport is only one aspect of what is needed to reduce transport emissions."
Currently, the contribution of renewable and low-carbon generation to the UK's energy supply was one of the lowest in Europe, said the report.
A range of new low-carbon energy sources was needed if Britain was to meet its renewables targets and ensure a greener power supply to electric cars.
These included new nuclear power stations, wind farms and tidal barrages.
Technical hurdles included the provision of economic high energy batteries, a practical solution to charging vehicles, and creating a large scale power distribution network.
A "smart grid" was also needed that could allow millions of vehicles to be recharged using low-carbon electricity without overwhelming local distribution circuits.
Richard Parry-Jones, a member of the working group and former Group Vice President of the Ford Motor Company, said: "Electric vehicles could provide a major contribution to meeting the target of an 80 per cent reduction in greenhouse gas emissions by 2050.
However, they will only be built in mass production numbers when there is a compelling sustainable social and business model for their use to allow manufacturers to plan for a long-term market and when the new vehicles have a real carbon efficiency benefit over the latest internal combustion engines."