When we accepted BMW's kind invitation to attend a launch in Spain, and, to ensure we had enough time with the car, drive it back to Britain, I really should have looked up Jerez in an atlas. Jerez de la Frontera (to give it its full name) is located a mere stone's throw from the Straits of Gibraltar on the southern-most tip of Spain. So essentially we agreed to drive the length of Spain, then the length of France before a quick train ride under the English Channel and a relatively short jaunt from Dover to home in Stamford. Did I mention that we needed to be back by Sunday lunchtime, with a departure of Saturday morning?

The choice of vehicle was important. At this particular launch BMW debuted the 630i, X3 2.0d and our steed: the 535d. Number one priority had to be comfort. The new 5-series has this licked, with electrically adjustable seats (for front passenger as well as the driver) and steering wheel allowing the perfect driving position, and minute adjustments can be made while underway to alleviate tension on such a long drive. I should add that the 630i is just as comfortable, but would require considerably more fuel stops than the derv-sipping 535d.

Both SE and Sport versions of the 535d were at the launch. The SE has the advantage in terms of ride comfort, with higher profile tyres and softer suspension settings, but we chose the Sport. Let's face it; the M5-mimicking body addenda and wheels seduced us. The keys to a classy 'Silver Grey' Touring were handed over after breakfast. With the satnav (excellent, but not cheap at £1,665 for the Professional system) set for Calais (a daunting 1,380 miles away) we set off in convoy with another three similar cars; all of us intent on having lunch the next day on home soil.

Small convoys are quite good fun over long distances; concentrating on where everyone is keeps you alert, and fuel stops for car and driver are far more entertaining in a group. The bonus for us of this BMW-labelled convoy was the chance to view the very car we were going to review in motion. It was a telling experience. Up front is an SE Touring in black, obviously from good stock, but not bullish about it. The styling of the 5-series is less opinion splitting in Touring guise. On roads that none of us knew, even when the Spanish motorways happened to incorporate a few amusing hairpins, the SE never looked out of its depth next to the stiffer Sport cars. Other than the Sport Touring we piloted, the other two cars were Sport saloons: the first in a pseudo-black shade of green and the other in limelight stealing 'Milano Red'. Without actually having a new M5 on hand to directly compare, this 535d Sport could easily be mistaken for the super M-saloon.

BMW revealed some interesting facts about the Sport 5-series at its presentation the night before. Apparently, 60% of buyers of the previous generation 5-series opted for the Sport pack. Accordingly, the Sport tag is now being marketed as a model range in its own right and BMW expects up to 70% of 5-series customers to buy a Sport model.

So what do you get for your £2,625 premium over the standard 535d SE? For a start, the aesthetics are given an incredibly effective overhaul. The 'M aerodynamic package' includes front and rear bumper changes as well as side sills and shiny exhaust pipes. Out go the 17-inch 5-spoke wheels and on go a gorgeous set of M-division 18-inch alloys, not too dissimilar to the 19-inch design fitted to the M5. At a standstill these wheels look beefy enough, but in motion they look even more impressive and greatly enhance the 5's stance.

Inside, the M badge is used on the tactile three-spoke leather rimmed steering wheel and on the scuff plates on the doorsills. The seats are tagged as sports seats too though I prefer smaller pews for my (ahem) racing snake-like frame. The Sport models gain 'aluminium cube' interior trim, which does brighten up the otherwise sombre interior and is lovely to touch, but the machined pattern in the aluminium may be a little extrovert for some buyers.

As an enthusiast, you would hope that the Sport badge brings more than just aesthetic and equipment changes; it does. Nestled behind the impressively proportioned brake discs is the M Sports suspension, incorporating stiffer springs and bespoke dampers as well as a reduction in ride height. Other choice parts are shared with the M5. It adds up to a sharpened chassis, though still cosseting - not noticeably less comfortable than the SE version we had a brief drive in.

Sport range aside, the main focus of our epic trip lies under the lightweight aluminium bonnet. BMW's nomenclature can be a little puzzling. The 530d has been around for a while and as you'd expect it is powered by a 3.0-litre diesel powerplant. Naturally the 535d is a 3.5-litre, right? Erm, no; the 535d's engine is actually a development of that fitted to the 530d and it maintains the swept volume. For the first time on a production diesel car, twin sequential turbos have been employed. BMW considers this as significant enough to warrant its own model number. Indeed Mark Harrison, BMW UK's Corporate Communications Manager, was quick to pre-empt questions about Jaguar's highly rated 2.7-litre twin turbo: that unit has a turbocharger per bank of its V6, with variable geometry vanes controlling the level of boost. BMW obviously thinks that its engine is better, using a small turbocharger at low revs for instant response, a large turbo at high speed and load, and a combination of both in between. The proof as they say is in the strudel.

BMW's straight-six puts out 272bhp at 4,400rpm, which is ample for a car that weighs about 1.8 tonnes unladen. Don't forget that peak power only really comes into the equation when you have the pedal to the floor. Mid-range power is more appropriate, and therefore the peak torque number is more relevant to the average driver. The engine in the 535d Touring pushes out an M5-beating 413lb.ft at 2,000rpm. Perhaps more remarkable is the delivery of 384lb.ft at just 1,500rpm.

On our drive, the 535d's engine was crushingly effective. There is no discernable lag anywhere in the speed/load range whatsoever. At idle, with the stereo off, the engine can be heard, but it is no tractor unit. Most of the time the straight-six is quiet, though there is what we think is injector noise at very high engine speeds when you have buried the accelerator pedal.

The sheer go is quite breathtaking, allowing easy and safe overtaking as well as comfortable long-legged cruising. The six-speed auto fitted to our car is the best automatic gearbox I have encountered; it shifts seamlessly in fully automatic, Sport or manual modes, which is quite a feat given the loads being transmitted. Other than for experimentation, I never found a valid reason to use the manual option. When tackling the twistier sections of Spanish motorway or squaring up to the aggressive drivers on the Peripherique around Paris, the Sport mode was just perfect, speeding up the throttle response as well as being keen to use the lower gear ratios.

The 'box aided rapid getaways from the many toll booths we encountered too. Indeed, accelerating from a standstill is mightily impressive in the 535d - it hits 62mph in only 6.6 seconds (or 6.5 in the saloon). However, I was more impressed by the accelerative forces generated even when deep into three figure speeds. Most cars rate of acceleration slows when a higher cog is selected; not the 535d - the engine seems to move the car to a point on the horizon you previously thought to be very far away. It is actually more enjoyable to drive the 535d at part-load and utilise the huge reserves of torque rather than pushing the engine to its red line.

Though not a direct rival thanks to a lower purchase price (even the most expensive 2.7-litre diesel Jaguar is £4,000 less than the entry-level 535d), the Jaguar's unit is claimed to produce 206bhp and 320lb.ft of torque, though the peak torque is produced at merely 1,900rpm. The only other potential competitor for the 535d (other than petrol cars - Jaguar's S-type R for instance...) we can think of at the time of writing is the Mercedes-Benz E-class 320 CDI, available as a saloon or estate. The Mercedes is a little less expensive to buy, though is certainly not as driver-focussed as we found the 5-series to be and has less power than the Jaguar diesel, though an impressive peak torque figure. I suspect both companies have already started thinking about the next development of their engines in an attempt to keep up with BMW. And where is Audi's answer?

The driving dynamics of the BMW 5-series should be touched upon in this test. BMW proudly calls each of its cars " The Ultimate Driving Machine"; therefore it has a duty to people like you and me to deliver on that. A driving enthusiast will instantly like the 5-series. Away from motorways, the 535d was a real hoot to drive quickly. In the dry, you can boldly turn off the traction control systems, as the steering feedback gives you the confidence to explore the outer limits of the chassis in the 5-series. Even the heavier Touring (nearly 100kg heavier than the saloon) resists understeer, and that amazing engine has enough low-down grunt to break traction for you to enjoy a little controllable oversteer. We reckon it would make a great drift championship contender!

As incredible a car as the 535d is, we still managed to find fault. Spanish motorways, and indeed most other roads in the country, are not very consistent. There are an excessive number of expansion joints, mixed surface finishes and lateral ridges. The latter in particular upset the composure of the 5-series, in extremes allowing movement away from the intended path. Though disappointed, I assumed that this characteristic was a symptom of the M Sports suspension and low-profile tyres fitted to the Sport; it turned out that the SE suffered the same problem.

We prefer to give our final views on a car once we have driven it on our own test routes in the UK. There are remarkable differences on the roads between countries. For instance, the problem described above evaporated once we hit the superbly surfaced French Autoroutes, but we were anxious as to how the Sport would perform in the UK - one of its most important markets.

We need not have worried. A few days after returning home I took the Touring down our favourite B-roads - a challenging assortment of surfaces, cambers and undulations: perfect for testing any car's composure as well as its ability to entertain. That the 535d came out the other side with a grinning driver at the wheel was not in doubt; the direct steering comes into its own on this sort of road, allowing rapid direction changes. The 5-series's chassis relished the challenge too, encouraging a neutral-to-oversteer attitude, even through the quicker, well-sighted curves. Bumps were soaked up and body control is exemplary, with only the mildest wheel hop betraying the topography of the tarmac. The brakes managed to be fade free, and the pedal feel itself is just divine.

To the surprise of my better half I rolled into bed before breakfast on Sunday, with nearly 24 hours gone by in the 535d. I was surprised to note that the car averaged 32mpg despite a consistently high cruising speed. I surprised myself further later that day by looking forward to getting back into the BMW and I even enjoyed the mundane task of helping a friend move house. There can't be too many cars that can tick all your boxes in the way the 535d Sport Touring did mine. Hell, I even took the long way home.