The latest data from the firm shows that more than one in four (26.4%) of the cars that it supplied in the first half of 2010 were rated at 119g/km of CO2 or less. A total of 8% of Alphabet orders this year were for cars rated below 110g/km and 1% were for cars under 100g/km.

Alphabet estimates that cutting CO2 emissions made cumulative cost savings for its customers of £2.9 million in fuel costs alone between 2007 and 2009. The drive to lower-CO2 cars reduced fuel consumption by 3.3 million litres and carbon emissions by 8,750 tonnes.

The company forecasts that the continuing shift to lower-carbon cars will save its customers a further £3 million at the fuel pumps over the next three years, despite projected rises in fuel prices.

Paul Hollick, general manager sales development at Alphabet, said: 'These figures are fantastically encouraging for our customers and for the environment. The cars we supply today are 16% more efficient than those of five years ago. That means customers are spending less on fuel, in real terms, despite the huge increase in pump prices. We have been working with our customer base for some time, helping them set policy, review total cost of ownership and reduce cost. It is good to see the tangible outputs of these policies that were put in place in 2009.'

Alphabet also expects to reach another milestone later this year, with the average CO2 rating of cars purchased by the company forecast to fall from its level of 140.2g/km in June 2010 to below 140g/km over the remainder of the year. As well as saving on fuel costs, the reduction will cut CO2 emissions by an estimated 13,000 tonnes.