DRIVING one of the latest Mercedes-Benz E-Class cabriolets - among the smartest choices on the road - it is hard to imagine feeling blue.

But blue is definitely the colour when behind the wheel of this impressive car - not a sad shade but pure blue efficiency.

The reason being that the E350 CDI Sport Cabriolet I was driving - a £53,000 package of power and luxury is one of the latest BlueEFFICIENCY models from Mercedes which have been tweaked for economy as well as power.

This totally impressive drive embraces the Mercedes-Benz BlueEFFICIENCY philosophy with a model that provides a combined mpg figure of 40.4mpg in seven-speed automatic form.

And a CO2 readout of of 189g/km underlines the fact that this car can also cut the mustard in a world where environmental friendliness runs hand in hand with pure unadulterated luxury and power.

Engineers from every Mercedes development department have worked together to optimise numerous assemblies and components, to save fuel by means of reduced weight, a new shape, improved functioning or efficient energy management.

Other BlueEFFICIENCY measures include lower rolling resistance, need-related and therefore energy-saving control of the alternator, fuel pump, air conditioning compressor and power steering.

The 2,987cc six-cylinder diesel is a latest-generation common-rail high-pressure direct-injection unit with 231bhp on tap and with a transmission featuring a sport mode as well as economy there is much punch there when you need it.

The Sport specification provides sharper acceleration response, continuously variable damping for improved rise and faster gearshifts via steering wheel paddles. This translates into a 0-62mph sprint of 6.9 seconds and with most cars in this category top speed is limited to 155mph.

With interior trim in high quality materials, this is one of those rare cars that makes you reluctant to step out of it into the hustle and bustle of an everyday world.

It is packed with technology, much of which is standard and the hood retracts neatly into the boot at the touch of a button.

This really is a glamour wagon par-excellence but the interesting thing is that it does it all in the best possible planet friendly way.

The basic on the road price of this car is £42,000 and at that it has a sky-high standard specification. A raft of options, including a £2,230 COMAND multimedia system and £1,370 for leather seats hiked it up to £53,110 - a tidy sum which buys you a stunning open top four-seater which is smart in more ways than one.