You can't escape the fact. As an antidote to insomnia, Volkswagen's Passat diesel has been hugely successful. Even if you've read this far without your eyelids feeling heavy, it's either because you've recently ingested a crate of Red Bull or you're a very strange fish indeed. As a reward for your perseverance, Volkswagen now make a Passat diesel line up that's significantly less boring than before. They even mention the 'e' word - exciting - in their promotion for the car, although that may be getting a little overenthusiastic.

It's easy to see where the normally reserved suits are coming from. The current Passat is a whole lot slicker than ever before, borrowing plenty of design cues from the magnificent Phaeton. That chunky C-pillar, the dashboard layout and the sculpted rear lights all smack of Volkswagen's bold but ultimately ill-starred foray into the luxury martket. Although the look may raise a few pulses, the diesel engine line up was initially rather bread and butter stuff.

It's starting to flesh out nicely though now, with the introduction of a 170PS version of the 2.0-litre TDI unit. This powerplant slots just above the existing 140PS unit. No V6 (and definitely no V10) TDIs on the horizon yet though. The old 105PS 1.9-litre TDI continues at the foot of the range. For the family buyer looking for a car that mixes practicality with a dash of panache, the Passat diesel makes great deal of sense. Saloon prices in basic S spec start from £16,545 for the 1.9-litre version and from £18,190 for the 2.0-litre model. Both engines are also offered in plusher Highline guise, while the 2.0-litre also comes in racier Sport trim for £20,970. An Estate is also offered at a premium of around £1,100 for buyers seeking greater carrying capacity and there's the option of 4MOTION four-wheel drive if you go for the TDI 140 unit. If fuel economy is everything, then ask about the 'BlueMotion' version of the 105PS 1.9-litre TDI model, a car that manages to eke over 54 miles out of every gallon, yet puts out just 136g/km of CO2 into the atmosphere.

All engines are Euro IV-compliant which means that company users don't get stung for the usual three per cent taxation surcharge and the rest of us can drive around with a warmly sanctimonious air, knowing that we're doing our bit for the environment. The emissions figures of 157, 159 and 181g/km respectively for the 1.9 TDI and 2.0 TDI 140 and 2.0 TDI 170 engines are among the class best. The 1.9-litre car is fitted as standard with a five-speed gearbox but the 2.0-litre TDI models get six cogs as standard with the option of the revolutionary DSG twin-clutch sequential gearbox.

"The Passat TDI now appeals to the heart as well as the head"

Volkswagen have made great strides concerning the refinement of these TDI engines and the effects are palpable as soon as you turn the key. The TDI system was once derided as being far less effective than the new wave of 'common rail' diesel engines that have become popular and in terms of refinement, Volkswagen's solution has lagged behind. No longer: the difference is now virtually negligible.

If you're interested in the technicalities, all three of these Passat diesel engines work on the basis of so-called direct injection, a system intended to make better use of every drop of diesel. The injectors on all four cylinders are controlled by a single powerful electronic control unit (ECU) which carefully controls the amount and mixture of fuel passing through into each cylinder. For engineers, the obvious next step is for each cylinder to have its own ECU unit; the fuel amount and mixture can then be even more carefully monitored and even greater efficiency achieved. This is the basic concept behind the new 'second generation' of 'common rail' diesels - engines that Volkswagen says it's developing in its own time. The big bonus of Volkswagen's TDI system is that it's relatively easy to liberate big power outputs.

Team the 2.0-litre TDI with the revolutionary DSG (Direct Shift Gearbox) and you'll have a very satisfying ride. This uses a sequential manual gearbox in order to ensure efficiency and rapid responses, but it also uses a clever twin clutch system to ensure creamy smoothness. Engage first gear and the gearbox will pre-engage second gear in advance, the second clutch engaging as soon as you flick up to fire the Passat instantly into second gear. This means a seamless flow of power. The electronics predict what gear you're about to engage, depending on whether you're accelerating or braking, and the result is astonishing, making every other gearbox look distinctly clunky. The other option is to slip it into 'D' and drive it like a normal automatic. Even in this mode it's butter smooth. One comes away with the impression that some day all gearboxes will be made this way. The petrol cars have to make do with the less special six-speed tiptronic automatic.

The Passat's cabin might come as a surprise to those expecting the Phaeton-esque styling influences to continue indoors. In fact, it's rather functional, albeit in a clean, uncluttered fashion. Somewhat unusually for a Volkswagen, this could be where rivals will seek solace. There is a good deal more use of light tones than in the unremittingly dark dashboard of the previous generation Passat, but those looking for something that signally moves the game on in terms of design philosophy may well come away disappointed. There are a number of technical highlights featured, however, such as Bluetooth connectivity for the telephone unit, a superior quality stereo, an electronic handbrake and a 2Zone Climatronic air conditioning system.

With prices starting from just over £16,500, it's tough to buy as much presence and capability for this little. To put it into perspective, a poverty-spec entry-level Mercedes C-Class diesel will demand nearly £24,000 of your disposable income. The Passat is newer, bigger, smarter and more powerful than the redoubtable Mercedes and in all aspects other than residual badge equity will make the better buy. Exciting? Maybe not. Inviting? Most definitely.