The BMW 3 Series diesel range is proliferating. The choice was once quite simple. You either chose a 320d (brisk) or a 330d (rapid). Nowadays it's a little more complicated. As well as the 318d (tepid) and 335d (ballistic), there's also now a 325d that packs a hefty 197bhp and might just quietly be the pick of the bunch.

Not that you'd ever guess in terms of column inches generated. This is BMW's invisible 3 Series, the model that everybody overlooks. Compromise has never been a dirty word in Munich and the 3325d offers all the real-world performance most customers will ever need, all backed up with admirable fuel economy, laudable emissions and a price tag that merits further investigation.

Offered in both four-door saloon and five-door Touring guises, prices start at £27,885 for the SE saloon rising to £30,525 for the M Sport trim level. The Touring versions are, model for model, £1,180 more expensive. How does this slot the 325d into BMW's current price structure? Taking the SE saloon as a baseline, it makes it around £2,300 dearer than the 177bhp 320d and £2,400 less than the 231bhp 330d. So, it sits virtually equidistant between these models in terms of price and, offering 20bhp more than the 320d and 34bhp less than the 330d, it splits them fairly neatly in terms of power output too.

The bhp-per-pound factor sticks to a law of accumulating returns. You'll pay £146 per bhp for a 320d, £141 for each 325d horsepower, £131 for the 330d and a mere £117 for the 335d. Just for fun and a point of reference, each horsepower in a 1.0-litre Citroen C1 costs £103 and those of the most expensive motor around, the Bugatti Veyron, are a cool £850 apiece.

But I digress. With 197bhp and a hefty 400Nm of torque at its disposal - as much as the old V8 BMW M5 - this is a car that asks whether you really need to splash out extra on more engine that you'll rarely if ever require. Yes, more of everything is always fun but when you're footing the bill, you've got to strike a balance and the 325d is an extremely well-judged balance point. It will accelerate to 60mph in a mere 7.4 seconds and keep going to a top speed of 146mph. The best part is that despite this punchy performance potential, you'll still be able to average over 47mpg with a measured right boot. Company car drives will also warm to the 325d as it offers emissions pegged at just 155g/km in saloon guise and 158g/km for the Touring model.

"The 325d could well be the surprise package of the 3 Series diesel line up"

The 2.5-litre six-cylinder engine offers the sort of smoothness you'd expect from one of BMW's latest generation diesel engines with a broad spread of torque meaning that you won't need to continually shift gears to keep it on the boil. Like all E90 3 Series models, the balance of weighting between the steering and the slick six-speed gearchange, together with the effort required to depress the various pedals, is all beautifully judged. The spacing between those pedals, the driving position and the sightlines out of the cabin all lend the belief that the 325d was screwed together by a manufacturer who deeply appreciates the finer aspects of building a car. Drive other rivals and you'll see how quickly they drop the ball in these apparently fundamental regards.

The starting process is slightly convoluted, and involves slotting the plastic key unit into the dashboard and then pressing a starter button to fire up the diesel unit. After the first couple of times you do it, the process seems a bit of an unnecessary work up, but the rewards are well worth it. The engine's torque comes in long, smooth streams and the engine disguises its turbocharged roots very well, feeling like a bigger normally aspirated unit to drive. The thing that really impresses is how much work has gone into making the car feel suitably premium.

Developing this generation 3-Series shows that the money men and the stylists went head-to-head in the battle between shifting big numbers and continuing the trend for challengingly styled BMWs. It seems that the stylists have blinked first, the 3-Series looking a good deal more conservatively penned than the rest of the BMW line up. Although those wearing the black polo necks may grumble, it's a wise choice. With the 3-Series accounting for fully 52 per cent of BMW's UK sales, alienating this bedrock of customers with a wilfully odd looking car was never going to make a sound business case. Although sales of the latest 5-Series have swelled as people became used to its sharky lines, for the first few months that styling was manna from heaven for Mercedes and Audi.

The practical advantages of the Touring version over the saloon only really make themselves felt when there are less than four people in the car. You get a 460-litre void back there to fill with the paraphernalia of your choice and that doesn't compare at all favourably with the 460-litres you get in the saloon for £1,180 less. Fold the rear seats down, however, and the available space mushrooms up to 1,385 litres. Forget about taking garden rubbish to the council tip or shifting that chest of draws home from the furniture store, you could hold a wedding reception back there or have it converted into a squash court. All right, I exaggerate but you get the point: it's usefully big.

The 3 Series Touring's 60:40 split-folding seats open up the possibility of seating a passenger in the back while still maximising the available loadspace and there are other practical features included in the package as well. Most notable is the split tailgate which opens up two different cargo access options by opening up in two sections.

The 325d gets the job done unobtrusively and with a minimum of fuss. Beneath that veneer of ever so slightly boring efficiency, there lies a car that's absolutely astonishing in the way it offers performance, handling and economy in equally impressive measures. Some vehicles need to make a big fuss to get noticed. If, like the 325d, you're playing an unbeatable hand, you don't need to shout about it.

TOP 5 3 SERIES DEALS

The results below show the top 3 SERIES deals on buyacar

	BMW 3 Series 325d SE 5dr Touring Estate
	ETR	Mthly	Saving £1,721	Price £27,449
	BMW 3 Series 325d M Sport 2dr Coupe
	ETR	Mthly	Saving £439	Price £32,471
	BMW 3 Series 325d M Sport 5dr Auto Touring Estate
	ETR	Mthly	Saving £2,110	Price £31,360
	BMW 3 Series 325d SE 4dr Saloon
	ETR	Mthly	Saving £1,614	Price £26,376
	BMW 3 Series 325d M Sport 2dr Convertible
	ETR	Mthly	Saving £624	Price £36,851