Latest registration figures for plug-in vehicles confirm the U.K. government's ultra-low-emissions incentive scheme is failing to ignite the market, the British Vehicle Rental and Leasing Assn. says.

It cites newly published Driver Vehicle and Licensing Authority data showing registrations of grant-eligible plug-in hybrid cars grew just 14% in first-half 2013, compared with the previous six months. This was less than the 17% growth achieved by the overall new-car market.

The association says registrations of grant-eligible plug-in vans fell 27% to just 119 units in first-half 2013 from 163 registered in second-half 2012.

Association CEO Gerry Keaney says the figures show the current strategy for driving uptake of ultra-low-emissions vehicles is not working.

The trade group is campaigning for PHEV users to be offered longer-term incentives such as a 10-year road-tax exemption, free parking and financial support when installing charging points at workplaces.

“The fleet market buys more than half of all new vehicles registered each year and operates the greenest cars and vans on U.K. roads,” Keaney says in a statement.

“As bulk purchasers, fleet operators could create a huge surge in demand for plug-in vehicles if they were given the right package of incentives. Unfortunately, the current tax regime actually encourages many fleets not to run plug-in vehicles.”

The government's Office for Low Emission Vehicles recently announced it would develop strong, clear and lasting tax incentives. “This work cannot happen soon enough,” Keaney says.

Association members operate fleets with a combined 2.75 million cars, vans and trucks, and buy nearly half of all new vehicles sold in the U.K.