Two of BMW’s most popular diesel engines are now available in the 1 Series Convertible. BMW’s most economical four-cylinder diesel engine ever and the award-winning twin–turbocharged unit are a timely introduction for new car buyers seeking open-air motoring but are worried about rising fuel costs.

The 118d Convertible is powered by a 1995cc single turbocharged engine producing 143hp and 300Nm of torque. This results in a 0-62mph time of 9.5 seconds and a top speed of 129mph. Most impressive though is the 118d Convertible’s ability to record a combined consumption figure of 57.6mpg and CO2 emissions of 129g/km. This means the vehicle, courtesy of BMW’s EfficientDynamics technologies, is the most economical and least polluting convertible car in its class.

For those customers demanding greater performance the 123d Convertible comes with a 1995cc twin-turbocharged engine producing 204hp and 400Nm of torque. This propels the 123d Convertible from 0-62mph in 7.5 seconds before going on to a top speed of 143mph. It too comes with all the facets of EfficientDynamics and thus records a combined consumption figure of 52.3mpg and CO2 emissions of 144g/km – again the lowest compared to any competitor product.

Both models come as standard with a six-speed manual gearbox. The BMW 118d Convertible is priced from £23,660, while the BMW 123d Convertible starts at £28,105.