Back in 1975, Mercedes-Benz launched a mighty beast of a car. It is sometimes said to be the best Mercedes ever made. The model in question was the legendary 450SEL 6.9, which, as its name suggests, was a variant of the S Class, fitted with an enormous 6.9-litre V8 petrol engine. Supercar and saloon in one, it incorporated a host of advanced technical features. Such was its sporting appeal, the British Formula 1 champion James Hunt became a notable fan.

According to my copy of Werner Oswald's Deutsche Autos 1945-1975 – Eine Typengeschichte, the standard reference work for post-war German cars, this magnificent machine had a top speed of 140mph and could accelerate from rest to 62mph (100km/h) in 8.5 seconds.

But not everyone who drove a Mercedes in the mid-Seventies had this sort of go at his disposal. Take the average German taxi driver in a 220D, for example. That car produced a miserable 60 horsepower, just enough for a 0-62mph acceleration time of 29 seconds and a top speed of 83mph. I don't think many racing drivers ordered one of those.

This week, our readers test the direct linear descendant of the old 220D. Like its predecessor, the E220 CDI has a four cylinder, 2.2-litre diesel engine and is the German taxi trade's workhorse of choice. Of course, you won't be surprised to learn that turbo-charging, common rail technology and other advances mean that today's car is a lot quicker than the 220D. ...more