Subaru Diesel

Famed for its go-anywhere four-wheel-drive transmissions and petrol-powered boxer engines, Subaru has never chased environmental honours.

But in 2007, company bosses were finally forced to cave in to demand – particularly in the European market – and unveiled their first-ever diesel engine.

This at last gave Subaru some green credentials – although as ever, engineers at the firm didn’t take a conventional approach. The new oil-burner was constructed with the same four-cylinder, horizontally opposed boxer layout as Subaru’s petrol units.

The engine was designed this way to keep the car’s centre of gravity low, so as not to upset the handling balance. It’s smooth and refined, too – but most importantly of all, it’s impressively efficient. And that has allowed the firm to compete with mainstream rivals.

Available in the Impreza, Outback, Legacy and Forester models, the 148bhp diesel powerplant delivers claimed combined economy of between 44.8mpg and 50.4mpg, depending on the model. It also promises low CO2 emissions. In the Legacy, buyers can expect the unit to put out 148g/km, and this rises to 167g/km for the Forester SUV.

A low-capacity petrol engine is also available in the Impreza hatch, although this 1.5-litre produces a surprisingly heavy 176g/km of CO2 – well behind class leaders.

The cleanest Subaru is the characterful 1.0-litre Justy, which promises 56.5mpg and 118g/km. But we’d opt for the more versatile diesel Impreza, with its figures of 47.9mpg and 155g/km.

BEST ECO BUY: Impreza 2.0d