The main difference is that while a conventional car's emissions come out of the vehicle's exhaust pipe, those created by an electric car are generated at the power station which supplies the electricity.
The findings come as the first ever electric car to pass the European crash test was announced - the Mitsubishi i-MiEVsuper-mini - getting four stars out of a maximum five.
Experts at Which? compared the carbon dioxide created by charging electric cars with that emitted by the most efficient diesel models and concluded:'Sometimes there’s not a great deal of difference.'
And the gap is narrowing as 'conventional' cars up their game to cut emissions.
The Which? report noted:'The common manufacturer claim that electric cars produce ‘zero emissions’ ignores the fact that most drivers use a conventional electricity supply to charge them, which has a carbon cost from burning fossil fuels. '
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