Switching to electric vehicles will not on its own have a significant impact on Britain’s carbon emissions, a report said today. Success depended on the availability of ‘‘green’’ electricity and overcoming a number of major technical problems, said the Royal Academy of Engineering. Professor 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.