Environmentally-conscious European drivers plump for diesel rather than hybrid vehicles, according to the findings of Car magazine.

Diesel-powered car sales have doubled in the past seven years, and are expected to make up half the total sold by 2006. A 20 per cent fuel efficiency advantage over petrol makes the fuel especially attractive to consumers.

Hybrid cars, sold only by Honda and Toyota, are more expensive, and their recent introduction to the market means they have not penetrated the popular consciousness.

However, a proposed new set of emissions regulations - which would have the effect of making diesel cars more expensive and less fuel-efficient - could change the market's complexion.

'There is clearly a risk that new emissions [regulations] increase the cost at the disadvantage of diesel to gasoline' said Renault chef executive Louis Schweitzer last month.

The hybrids, which offer 66 miles to the gallon, according to Toyota, would definitely become more competitive if the price of diesel were to be increased, although the gap between fuel sources would remain.

A diesel engine currently costs around EUR900 (£630) more than a petrol one, while mild (small motor) and full hybrids cost EUR 1,800 and EUR2,500 more respectively.

Toyota executive vice president Akihiko Saito said that if diesel and petrol had equal nitrogen oxide (NOx) and particulates emissions standards, current diesel technology would be priced out of the market.

'European manufacturers are trying to emphasise their European [diesel] technology', he said. 'But it is predicated on rather lax NOx regulations on diesel compared to gasoline.

'If those NOx regulations are brought into line much more effort will be needed for diesel. The diesel-driven cars' cost could be higher than gasoline-driven hybrid vehicles'.