Plans for the government to pay subsidies of £2000-£5000 to plug-in hybrid and electric car buyers from 2011 have been dismissed by political rivals as a gimmick.
The primary concern is that electric cars will be expensive and impractical without a much more developed support system, including a national recharging network.
However, George Osborne, the shadow chancellor, said that the government's announcement was "fantasy" because it lacked the detailed planning to sustain the increased number of new electric cars that would hit the roads.
Under separate Conservative plans, he said, there would be investment - to be accompanied by £30 billion in private funds - in a smart electricity grid, recharging points and high-speed rail.
Osborne said, "The government's announcement does not seem to include any of the crucial measures that are actually needed to make electric cars a mainstream reality.