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Also known as Plug-in Hybrid Electric Vehicles (PHEVs), plug-in hybrids are similar in design to conventional Hybrids except their battery can be recharged from an external power source such as electric vehicle charging points.

As a result they can travel significant distances, typically 40 miles, using just their electric motor before their internal combustion engine kicks in.

They are being widely touted as a means of cutting carbon emissions and urban air pollution, while improving vehicle fuel efficiency to a level where cars can travel upwards of 250 miles on a single tank of fuel.

A range of new plug-in hybrids are expected to be launched over the next two years, including GM's Chevy Volt and a new version of Toyota's Prius.

Plug in hybrids are expected to be more expensive than conventional cars, however they will result in reduced fuel costs and a number of governments are offering tax breaks to try and increase consumer take up.