We won't waste any time trying to pigeonhole the Mercedes B-Class into a convenient sector of the market. It's one of an increasing number of vehicles that defy categorisation by established means so it's better not to go down that road at all. What is clearer is that, be it a compact executive estate, premium compact MPV or prestige family hatchback, the B-Class is designed to provide practical family transportation. And, like other vehicles of this ilk, it's well suited to diesel power.

Here we examine the Range-topping diesel in the B-Class Range, the B200 CDI. Available solely in Plush SE trim at prices from £21,815, it isn't cheap and buyers at this level have a vast Range of different products within their reach that could perform a similar role. An extremely well-specified Renault Grand Scenic dCi would be an option, a BMW 320d Touring wouldn't be too far out of reach or how about a 2.0 TDi 140bhp Volkswagen Touran Sport along with over £1,000 left in your pocket? The B200 CDI goes up against some accomplished and very different vehicles but aims to carve a niche out for itself with its own particular set of qualities.

The engine first and it's the three-pointed star's 2.0-litre 4-cylinder 16-valve common-rail injection unit that's offered with a 6-speed manual 'box or the Autotronic self-shifting option. The claimed average economy of 50.4 mpg will raise a fair few eyebrows given the B-Class's ample dimensions and a 0-62mph acceleration effort of 9.6s is also to be commended. Top speed is 124mph and that should be plenty while CO2 emissions of 146g/km place the B200 CDI in a lower tax bracket than the entry-level B150 petrol model.

The B-Class handles neatly enough, with less body roll than you may expect for such a high-sided vehicle although the ride is on the firm side. The electro-mechanical power steering feels a little odd at first, but trust it and it'll direct the car's nose accurately. The diesel engine in the B200 CDI isn't the most refined unit you'll encounter with vibrations in the cabin and noise at higher revs becoming wearing over time but performance is more than adequate. The ESP stability control system can feel a little over zealous for real press-on driving but otherwise it's fairly vice free. With a little more weight to carry around than the equivalent A-Class, the B-Class enjoys better front end traction and the B200 CDI has little trouble getting its full quota of grunt down onto the tarmac.

"?average economy of 50.4 mpg will raise a fair few eyebrows?"

Sit in the back of the B200 CDI, stretch your legs out and you'll appreciate that it's comparable with the amount of room in the back of an S-Class limousine. Only those at the extreme end of the ergonomic scale will have any problems with head or legroom and there's ample room for three abreast. Despite this, the B-Class breaks the tape at only 4,270mm long. To put that figure into perspective, a Ford Focus measures 4,342mm from bumper to bumper, making this Mercedes something of a packaging marvel.

The rear seats all fold flat into the floor and the boot floor can even be raised to offer a flat loading surface. Other clever touches include a front passenger seat that folds forward to permit long loads and slots next to the rear doors to allow seat belts to be stowed safely out of the way when loading and unloading. The centre rear seat back can also pop forward, offering an armrest with a neat pair of cupholders when travelling four-up. The driving position is undeniably sporty. The wheel sits almost vertical and your legs stretch forward into a deep footwell. It almost feels like sitting in a jacked-up Lotus Elise but for the interior quality.

In order to best appreciate the great strides Mercedes have made with the B-Class, acquaint yourself with, say, an old A-Class or an early M-Class model. Open the glove box and observe how the hinges look only marginally more expensive than a CD case. Pull at the floppy plastics of the lower dash. Marvel at how Mercedes had the chutzpah to put a plastic gearchange selector in the M-Class that wouldn't pass muster in a Kia. The B-Class isn't quite back to the over-engineered Benzes of the Seventies, but it's as good as anything else out there in terms of perceived quality. Not only that, but the interior aesthetics are, to this eye at least, a lot happier than those in the latest BMW and Audi offerings.

The dashboard is cleanly designed with a neat mix of contrasting colours and metallic detailing. Standard specification across the Range includes air-conditioning, a four-spoke steering wheel with multifunction buttons, an armrest between the front seats, electric windows and tinted glass, Plus brushed aluminium trim on the fascia, transmission tunnel and door panels. Front parking sensors should have made the list too, as the front of the car slopes rapidly away and the body-coloured rubbing strips don't look as if they'd withstand too many scrapes with a concrete bollard before they started to look a little second-hand.

Mercedes would have us refer to their B-Class as a Compact Sports Tourer but there's not much that's sporty about it and so the relaxed nature of the CDI diesel engine suits the car well. The B200 CDI performs and handles competently enough but its biggest strengths are its interior packaging and the Mercedes-Benz build quality which seems to have returned to form in this instance. The 2.0-litre CDI powerplant does look expensive in the context of the wider market but everybody knows you pay a premium for the three-pointed star and the excellent fuel economy will at least help you recoup some of your outlay.