The Sports Coupe is all very well for an entry-level Mercedes diesel, but at the other end of the scale is the mighty new S320 CDI. Strict Euro IV emissions regulations due in January mean the firm's most costly oil-burner has had to clean up. But the model's refinement hasn't been affected by the changes.

Passengers will hear more engine noise in the S320 CDI than they would in the petrol S350, but the unit's growl isn't intrusive. What's more, the fresh diesel power plant is one of the smooth-est around. The 3.2-litre 201bhp six-cylinder engine pulls the saloon from 0-62mph in 8.2 seconds - the same performance as the outgoing model.