It's a sign of the times - after 15 years of production of its retractable hardtop (vario-roof) convertible SLK series, Mercedes has given the compact roadster a diesel engine. The 204 bhp four-cylinder delivers fuel consumption of 56.5 mpg/4.16 L/100km (combined cycle), but thanks to the 2143 cc diesel engine's 500 Nm midrange and 7G-TRONIC PLUS automatic transmission, the car offers a 0-100 km/h (62 mph) acceleration time of 6.7 seconds and a top speed of 150 mph (241 km/h).

The SLK 250 CDI's relative frugality at the pump is mirrored in its emissions performance, dumping just 132 grams (4.66 oz) of CO2 into the atmosphere per kilometer (0.62 miles) thanks to its fourth-generation common-rail injection and start/stop system.

The SLK 250 CDI will be available with all three versions of the vario roof and all three SLK suspension packages. It will look no different to the petrol models apart from the badging and will go on sale early in 2012. No pricing details are yet available.