The SLK 250 CDI has the 2.1-litre, 201bhp four-cylinder diesel engine from the C- Class, E-Class and CLS models.
In the SLK, it averages 57.7mpg; that’s a 14.9mpg improvement over the next most efficient petrol SLK model, the 250 CGI.
The SLK 250 CDI emits 128g/km of CO2, a 30g/km improvement over the 250 CGI. Company car tax is 18% for the diesel version, whereas the petrol falls into the 20% bracket.
A seven-speed automatic gearbox and engine stop-start system come as standard. Mercedes claims that performance is equivalent to a petrol engine that's twice as big, thanks to 369lb/ft of torque. It quotes a 0-62mph time of 6.7 seconds; 0.1 seconds slower than the 250 CGI petrol. Top speed is 151mph.
Externally, the 250 CDI looks like any other SLK model. The same range of options are available, including a 'magic sky control' roof, which changes from dark to transparent at the touch of a button.
Mercedes SLK 250 CDI gallery
Mercedes hasn’t confirmed the UK on-sale date or prices. The European model hits showrooms on September 13, from €41,829, which means UK cars should cost around £37,000.
The SLK 250 CDI will be part of Mercedes' display at the Frankfurt motor show next month, alongside the new B-Class and the SLS Roadster.