On the face of things, the Vauxhall Signum appears to be just a variation on the Vauxhall Vectra. It shares the longer wheelbase platform of the Vectra estate, some five inches longer than the saloon and five-door hatch body styles, yet at the same time does not have the load space of the estate model. Vauxhall justifies this by claiming that the Signum "combines premium saloon quality with the versatility of an estate and the flexibility of an MPV".

So much for marketing speak; what did we make of it? First impressions are favourable; our car, in 'Exclusiv' trim (second from bottom of four levels available) looked very smart in metallic steel blue with 18-inch alloy wheels and rear privacy glass. The Signum has been given a fresh new large-headlight face recently and it gives the car more personality. Inside, the disappointment of not having leather trim was countered by the massive rear legroom available, while still providing a decent sized luggage area behind. Closer inspection of the rear showed that although seat belts were in place for 5 passengers, the rear seat was designed to favour four passengers, with the fifth being very much an occasional seat only. The central seat can be tipped over to supply cup holders for the outer two passengers.

The Vauxhall Signum 1.9 CDTi model is available with a choice of two diesel engines, one with eight valves giving 120bhp and the other (as tested here) with 16 valves and a claimed peak power of 150bhp. The 16v engine option adds just £500 to the price of the car (£20,495 in this trim) and would seem to be a no-brainer if you plan to go down the diesel route. Sixteen valve Signum diesel owners get a six-speed manual gearbox with the option of a six-speed automatic transmission. The Signum is available with front-wheel drive only.

The engine itself suffers a Jekyll and Hyde characteristic. Off boost, it is painfully sluggish, yet once 1500rpm shows on the rev counter, the Signum pulls quite strongly; at least it does in contrast to its lack of pull below 1500rpm. This isn't a problem at all on the open road, but driving round town, traversing housing estates and in regular stop-start driving it became much more disconcerting. If you slowed for any reason, for instance coming into a junction, or up to a parked car, and then meant to drive back off again, the Signum would have fallen off boost and be sluggish to the point of almost going nowhere. This necessitated a quick gear change down at which point it would almost uncomfortably lurch forward with much marked vigour making town driving a little less smooth than it might be.

Out on the open road, it was a different car completely. Despite inordinately high gearing which meant sixth was rarely used below 50mph (and urban limit driving was normally carried out in fourth), once freed from the shackles of the urban environment, the Signum diesel felt plenty quick enough to maintain pace, to overtake briskly enough, and all without ever needing to change gear. The high gearing also means the Signum is endowed with a massive range between fill-ups. Despite only having a 13.2 gallon fuel tank (60 litres to you metric kids), I managed over 500 miles without filling up, and the trip computer still estimated 28 miles to go. What this was 28 miles to, I wasn't overly sure - the fuel gauge was just on the point of falling into its last segment (it is broken into eighths) and thus suggested there should be more like 1.5 gallons to go. Whichever way, real world fuel consumption seemed to be around 40mpg which is very good for such a large car.

Throw in some corners, and the Signum doesn't protest, neither does it seem to relish them. Looking at the wide 18-inch alloy wheels and 225/45 R18 tyres, you would expect a sporty bias to the ride and handling of the Signum, but that's not what you get; it's perfectly capable but no more than that. The wheels look great but I couldn't help thinking something more conservative would add to the ride quality (pretty good despite the 18s), more than it would detract from the cornering. The Signum is not a sports car, nor indeed a sporty car.

In Exclusiv trim, the Signum comes with full colour satellite navigation as standard. The unit also contains the CD-tuner and trip computer functionality, all sharing a screen mounted high in the centre of the dashboard. At first I thought it was a touch-screen system and wondered why I couldn't get it to obey, but once I fathomed that it wasn't, the system was intuitive to use and worked well. A postcode based destination search facility would have proven more useful than the town/street based search, but otherwise the system was simple to use and got me to my destination. A tie-up with Trafficmaster also means the system is capable of receiving live traffic flow information for the UK's motorways and trunk roads. The driver is able to scroll through the information to find those relevant - although a graphical system such as used by Trafficmaster themselves might prove more user friendly.

The audio system comes with seven speakers all round the cabin and despite only boasting 20 Watts/channel, seemed more than capable of delivering adequate sounds. This was probably aided by the Signum being a relatively quiet car. When being revved of course the diesel engine makes its presence heard, but at motorways speeds wind noise is fairly low, with tyre noise being the predominant aural aid to judging your speed. On concrete sections of the M25, tyre noise was a little louder than ideal, but on better surfaces the Signum proved a relaxed cruising machine.

The Signum's raison-d'etre is its flexible seating system, so a few words should be written about it. 'FlexSpace' seating means that the rear seats (individually) move forwards/backwards and also recline. As mentioned, the occasional fifth seat in the centre rotates to provide a wide armrest console with built in drinks holders. The rear seat splits 40-20-40 so many combinations of it can be folded down to provide additional luggage area. With the whole back seat folded down - it folds completely flat - there is 1410 litres of luggage space available. That is impressive, though I found a disadvantage for the shorter of us: the rear hatch opens very high and even the internal handle is a long way off the ground.

At night time, the bi-xenon headlamps proved to be awesome. On dipped beam they were merely excellent, with the added bonus of looking round corners with the steering. On main beam they simply lit up the whole world like giant searchlights and turned night back into day. A shame that this excellent vision is then betrayed by the Signum's blind spots. The rear view showed a long tunnel back to the rear screen; the privacy glass made looking over your shoulder for lane changes after dark somewhat hit-or-miss, and other cars seemed to hide from the door mirrors making motorway driving after dark more tedious than it should be.

Other than that, the list of complaints is short. The stereo always seemed to be on when turning on the ignition regardless of whether it was turned off at the end of the last journey. I guess this is a corollary of the 'infotainment' system controlling everything, but could still be annoying. I never did get on with the electronic indicator stalks that barely needed a touch to activate, and an even more subtle touch to cancel, but familiarity with them might improve matters. And finally, I thought the dashboard let down the prestige aspirations of the Signum and was at odds with the exterior (which looks very smart indeed). The dash was a mish-mash of different shades of plastic, all hard looking, and a couple of aluminium effect slashes just didn't work in my opinion.

The Signum 1.9 CDTi sits in a range of Signum models ranging from £18,735 up to £26,745. The Signum is available in four trim levels (Elegance, Exclusiv, Design and Elite) and with engine options of 1.8 16v, 2.2 16v, 2.0 16v Turbo and 2.8 V6 24v Turbo petrol engines, along with the two 1.9-litre diesel engines and a range-topping 3.0 24v V6 diesel. This is a large range of options in what I would have thought was a bit of a niche market.

A final note; Vauxhall was the first manufacturer in the UK to sell its cars over the Internet, and they still do, allowing the buyer to make a hassle-free purchase at a discount from the list price. Of course, a determined buyer could probably haggle a better deal face to face in the showroom, but the British car buyer is reserved and many find the haggling difficult. Maybe for these, an Internet purchase is a true money saver.