"A new breed of premium car . . . wholly original," runs the blurb for Vauxhall's quirky Signum. It's a common claim for a car manufacturer, but in this case it's closer to a fact than usual.The Signum isn't a saloon, because it has no boot; it's not an estate, because its cargo-hold isn't big enough to qualify; and yet it's not a hatchback, because it's too big to qualify as that. Perhaps a term like "megahatch"or "stretchatch" might be appropriate . . . or maybe not. (Editor's note: Office opinion is definitely not.) The Signum is not a completely original concept in that Renault has done something similar, if bigger, with its Vel Satis, but it's still uncommon enough to turn heads. At least, that's what I found when I took custody of one for a few days. This was the mid-level model Design with a manual five-speed gearbox and the frugal but useful 2.2 DTi engine - a turbocharged unit that turns out 123bhp in power and 206lb/ft of torque while pulling the bulky vehicle an average of 44.8 miles on one gallon of diesel. The official figures say it should reach 60mph just over ten seconds after take-off and run on up to a maximum speed of 125mph.I see no reason why this shouldn't be the case. It takes off from the lights with more than enough enthusiasm to keep up with most other cars on the road, but where it particularly shines is in its rolling acceleration. Ease your foot down on the pedal to overtake, and the Signum just surges out with measured, solid performance. I have no doubt that the car would cruise the autobahns of Germany all day at speeds up to 90mph without ever being over-stressed.All that is more than adequately kept under control by a wonderful suspension set up. Some commentators say the Signum is more at home on straight roads than it is out in the twists and bumps, but that's not my experience. Despite its size it corners flat and level, and with such confidence that you just want to push it harder, while on the straight the spring and damper set-up copes admirably with such vertical vagaries as sleeping policemen and back-road potholes.The electro-hydraulic power-assisted steering is perfectly weighted, and accurate enough to make best use of the available tarmac on the narrowest of twisting moorland roads, and the brakes, equipped with an impressive array of computer-aided enhancement programmes like ABS, CBC, EBD and EBA (I'll tell you about them some other time) are confidence-inspiring out there in sheep country without being harsh and snatchy about town.So it's a good solid drive that makes sense on the performance and handling fronts, but that's not what the Signum is all about; it's about the package that wraps around it. The company's promotional stuff uses single words as entire sentences: Stylish. Refined. Versatile. New. Original. It also talks about the car "delivering everything you need in life and doing so according to its own rules". I wish manufacturers wouldn't insist on promising so much when so few of the claims measure up to scrutiny. I actually liked the car a lot more before I read what it was meant to offer.Starting with the looks, it is well proportioned in a contemporary, semi-sporting way, with clean flanks, a smooth and raked window line, and a trendy wrap-around rear window. I have to admit that my test model was decked out with about £1700 worth of Irmscher body-kit to sleek it up a bit. The extras do look a bit costly, though, like the front spoiler (£401), the rear lower skirt (£450), the side sills (£534 the pair) and particularly the rather diminutive roof spoiler (£392).Inside, there's no doubt some effort has gone into making the Signum clever, but how much of that is just over-working and how much is genuinely useful, only you can decide. Personally, I feel that a large and roomy car being promoted as "delivering everything you need in life" could stretch to having five useable seats instead of the limited-use, multi-function flip-and-clip contraption that's in the middle in the back.Okay, both the main back seats are very comfortable, able to slide fore and aft, or partly recline independently, but the padded bump between them is only a seat for youngsters, and only on very short trips. It may have a three-point seatbelt secreted away on a magnet in what Vauxhall calls a "rather clever compartment" in the roof, but your kid would need buttocks of steel to cope with the squab they're strapped to.That squab tumbles back to reveal a cluster of little trays and two cupholders (well, you never know when you might need them) and an elbow rest drops forward from the back. While we're in here, though, it's worth noting the back seats all fold flat independently to increase the size of the boot, which is useful.In the front, the driver's seat adjusts manually in all sorts of directions, and it's very comfortable despite having no alteration on the lumbar support, but once again there's a feeling that it's been over-worked a bit. All the dials and buttons are pretty conventional, and there's a cluster of mini overhead lockers down the middle of the ceiling, which is probably useful for cards, sunglasses, sweets and the like.However, the split-level storage box cum elbow-rest between the front seats intrudes on your space in several irritating ways. I'm not being picky in saying it makes it more awkward to operate the handbrake (which incidentally is so close to the driver's seat that you're scraping your fingernails up the squab every time you engage it) and it leaves a tight gap next to your hip down which to stuff the seatbelt. If it's a wriggle for a slim chap like me to do the latter, anyone at all circumferencially challenged needn't even try.But that's about the end of the gripes, except perhaps the intrusion of the large and low rear-view mirror on the visibility to the front, and the similar intrusion of the C pillar on the rear three-quarter view.The Signum is well-equipped, even at this base level, with a fairly good built-in CD/radio, air conditioning, and an onboard computer that tells you, through a glowing screen, a number of things about your fuel consumption, speed and range. This model didn't have the CD ROM-based satellite navigation system my brochure tells me is now standard fit on all models, so a deal on prices may yet be struck on similarly lacking, brand-new showroom models. Engine 2172cc, 4 cylinders Power 123bhp Transmission 5-speed manual Fuel/CO2 44.8mpg / 170g/km Acceleration 0-60mph: 10.2 seconds Top speed 125mph Price £20,315 Details correct at publication date