David Cameron yesterday confirmed that he opted for a large luxury car, rather than a less polluting model, when he decided to ditch his Government-provided vehicle for environmental reasons.

His admission came as he announced plans to commit the Conservatives to targets to slash emissions of greenhouse gases from traffic on British roads.

As leader of the opposition, Mr Cameron is entitled to a Government car. But he has decided to hand back his Vauxhall Omega and instead lease commercially a more environmentally-friendly Lexus GS 450h with a "hybrid" engine which gives off less carbon in exhaust. However, he turned down a Government-provided Toyota Prius, whose emissions, at 104g per kilometre, are significantly lower than the 186g given off by the Lexus.

Mr Cameron said he had opted for the larger car because the Prius was not big enough to carry all his entourage, meaning he would often have had to take two cars on visits.

"My current car that the Government gave me is 276g, so the car I am getting is going to be a huge decline from that," said Mr Cameron.

"My problem is that often when I go on tour, I have a lot of people in the car with me and I found on the tour when I used a Prius it meant we had to have two cars rather than one, so I don't think it would be very good for the environment."

Mr Cameron is to commit the Tories to a target of cutting emissions to 100g a kilo-metre from new cars by 2022 and from all cars on British roads by 2030. In a weekend article he held out the prospect of "significant incentives" to encourage motorists to switch to environmentally friendly models.

This would encourage manufacturers to develop green technologies, like hybrid engines, new generation diesel and biofuel-driven vehicles, he argued. Mr Cameron said that he would today announce a "radical agenda for greener cars".

"I want Britain to be at the forefront of international efforts to build a new generation of motor vehicles that are much less environmentally damaging," he wrote.

"Such a programme will include significant incentives to encourage the ownership of newer, greener vehicles."

Mr Cameron declined to discuss what incentives he would offer and whether he would increase vehicle excise duties on high-polluting gasguzzlers or impose green taxes on air flights.

But it is thought that he may be considering lower car tax, reduced road tolls or cut-price parking for low-emission cars. He made clear that he saw Government's role as stimulating demand for environmentfriendly motors, rather than penalising gas-guzzlers or imposing restrictions on manufacturers.

"For Government the task is clear - to stimulate demand through a range of incentives.

"If enough demand is stimulated, manufacturers will bring forward new models and expand capacity."

He also shied away from cutbacks in road-building as a means of reducing traffic levels. "There is a need for some extra road capacity and there is a need in a growing economy to make sure people can get around," he said.