Government subsidies for electric vehicles are likely to remain unclaimed because demand for the technology is lower than anticipated.
Whitehall had estimated 8,600 claims to be made in the first year of the programme, but now admit that the anticipated demand has fallen short.
Up to £8,000 is available off the price of a new electric van but just 404 claims have been made since it was introduced in January 2012.
A total of £400 million was allocated to the fund to offer discounts on plug-in vehicles, but the Government now thinks just £230 million to have been claimed by the time the scheme is scheduled to end 2015, leaving £170 million in unclaimed subsidies.
According to a recent report by the Department for Transport, 6,709 claims had been made by the end of December at a maximum cost of £33.5 million.
In a written answer to a Parliamentary question, roads minister Robert Goodwill said: "Sales of ultra low emission vehicles have been increasing year on year, but at a slower rate than originally anticipated.
"We are currently projecting to spend circa £230 million over the period. Grant uptake in 2013 was 335% higher than in 2011, grants in January 2014 were at a record level and 679% higher than the equivalent month in 2013."