I was quick to agree with a friend who came over all squirmy when I parked the X-Type outside his house. It has been around for a few years now, and although quite a few elegant estate cars have been introduced more recently, I can't think of many which are quite as good-looking as this one.The same friend was rather disheartened when I mentioned that the X-Type uses the same platform as the last-generation Ford Mondeo, and there we differed. I know that a lot of people get very sniffy about this, but platform sharing does not lead to the production of identical cars, and there is nothing about the X-Type which immediately reminds you of the old Mondeo (not that it would be a big problem if there were).Right, that's that off my chest. On now to the test car, in which I covered more than 1200 miles in less than a week. You won't be surprised to learn that this involved a lot of motorway driving, and I've come to the conclusion that motorways are this car's home territory.From past experience of X-Type diesels I'm slightly surprised by this. I assume that there have been developments which Jaguar has not drawn much attention to, because in earlier tests I've complained about noisy engines and poor ride quality. This car was notably quiet - partly because 70mph equates to well under 2000rpm in sixth gear - and it wafted along major routes very comfortably.I wouldn't have believed this last bit the first time I saw the car. The Sport Premium comes as standard with 18" Proteus alloy wheels (which I must say look sensational) and low-profile tyres, and I was expecting a very jittery ride. As things turned out, though, remarkably little information about uneven road surfaces was conveyed into the cabin.The Sport Premium also has uprated seats, and if I had to nominate one reason for the car's serenity on motorways, this would be it. They are superbly supportive, especially at the sides, and they allowed me to keep driving without any aches or twinges for far longer than average.The larger (2.2 litres) and more powerful (158bhp) of the two diesel engines Jaguar offers for the X-Type (there's a 128bhp two-litre alternative if you're interested) sipped fuel at an impressively low rate. The official combined fuel economy figure is 45.6mpg, and according to both my own rough calculations and the readout on the trip computer I came pretty close to that.I got 560 miles out of the first tank, but not quite 500 from the second. Since there was a lot more country-road work during the second stint I wasn't surprised by the increased consumption; but in this period I had further confirmation that the X-Type was at its best on the motorway.Despite the impressive-looking tyres, and the sports suspension which comes as standard on Sport Premium models, this car just doesn't cut it on the difficult stuff. The rocking motion familiar from other front-wheel drive X-Types combines with a front-end bounciness (a clear case of insufficiently damped suspension) to produce very uncertain handling, to the point where you quickly feel that the chassis can't properly deal with much of the available 152bhp. The slightly clumsy clutch and gearchange actions of the early X-Types has never been improved, which doesn't help the situation either.It's quite a let-down. On a long run from one end of the country to the other, the X-Type feels a class ahead of other cars its size. From one town to the next it bears no comparison to cheaper rivals with far less impressive badges.Despite the reservations, it's difficult to dislike the X-Type in some ways. The interior, for example, may not have a particularly modern feel to it, but what it does have is a sense of refinement which is hardly matched in any remotely similar car.The Sport Premium is the best-equipped car in the 2.2d range, as well it might be with a price tag of nearly £29,000. Most of what you would expect is included in that sum, such as seat memory function, very smart leather upholstery, a folding rear armrest, cruiser control, automatic headlights and wipers and so on.Non-standard options fitted to the test car amounted to front and rear parking sensors (a splendid idea, though visibility is quite good at both ends), a premium sound system, powered folding door mirrors and carpet mats.Within that beautifully styled rear end there's a class-competitive 455 litres of luggage space, extending to 1415 litres when you fully fold the 70/30 split rear seat. The tailgate extends down to bumper level, so you don't have lift anything far off the ground to clear an awkwardly high sill, and if space is limited and you're carrying small and/or light goods you can leave the tailgate shut and just use the separately-opening rear window instead.Neither I nor my front-seat passenger had any complaints whatever about room, though two companions who sat in the rear were critical about the lack of space. It has been suggested that this is just because they wanted to sit in the front, but that may be a harsh view. Engine 2198cc, 4 cylinders Power 152bhp Transmission 6-speed manual Fuel/CO2 45.6mpg / 164g/km Acceleration 0-62mph: 9.3 seconds Top speed 134mph Price £28,900 Details correct at publication date