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.
"There's nothing about building a smart grid that can manage the higher demand for electricity that will result if more people are driving electric cars.
"There's too little on creating a national network of car charging points, so that motorists can actually drive their new electric car around the country.
"The Labour plan announced today is like giving people a grant to buy an internal combustion engine, without bothering to set up any petrol stations."
Norman Baker, Liberal Democrat Transport spokesman, said, "This announcement is like adding a small dab of green paint to the rusty hulk of the Government's failed transport policy.
"Discounts on electric cars are all very well for those who can afford to buy a new car but it cannot hide the fact that the Government has forced up rail fares and destroyed many local bus services.
"This might have been a sensible policy if it was part of an overall climate change strategy, but on its own it is just a gimmick."