It seemed oddly appropriate that we drove past a road sign directing us to Augsburg. In 1897, it was in Augsburg, at the Maschinenfabrik Augsburg-Nürnberg (or MAN as it’s better known these days) that Dr Rudolf Diesel first got a compression-ignition engine to work properly. It was an engineering feat that revolutionised the world of transport, supplanting coal-power both on the railways and on the high seas, not to mention creating those endless queues of heavy trucks that now daily traverse the entire continent. And, by roundabout way, it gave us the diesel car - once seen as the low-carbon, frugal-fuel saviour of the modern motoring age.

Now though? Diesel’s reputation (both of the man himself and the engines he fathered) now lies in tatters, brought low by scandal and recrimination, and revelations of all the diesely gunk we’ve been sucking down into our lungs on city streets across the world.

We were swishing past on silent electric power, bypassing Augsburg both literally and figuratively to enter what, hopefully, are the sunlit uplands of the future of electric and part-electric motoring.

Plugin hybrids are nothing new, of course. Toyota first showed a work-in-progress Prius plugin half a decade ago, while the technology is now becoming commonplace in SUVs both large (X5, XC90, Q7) and compact (Mitsubishi Outlander). Volkswagen has been hard at work putting plugin tech into the Golf, Passat and Audi A3. Somehow though, this feels more significant.

3-Series plug-in

The BMW 3 Series has for so long now been the go-to car when it came to naked desire. A diesel 320d is still the most-searched for car on second hand websites in Ireland, and why wouldn’t it be? Slick, Germanic looks. Deft, rear-drive chassis and the promise of 55mpg in daily driving. No wonder everyone wants one.

The 330e which just left the Augsburg turning behind, though, could just be the 320d’s undoing, thanks to the Irish vehicle taxation system. Here are the raw figures. A 330e comes with a 184hp 2.0-litre four-cylinder turbo petrol engine, backed up by an 88hp electric motor, both driving the rear wheels. Combined, the system produces a very healthy 252hp (more or less the same as a petrol 330i) and 420Nm of torque (almost as much as a petrol 340i). 0-100kmh is done with in 6.1secs. So far, so 3 Series. But if you charge its compact battery stack (located under a truncated 360-litre boot) from the mains (takes about three hours) then you can go for a claimed 40km on just the batteries (at speeds of up to 120kmh) and BMW claims that, on the current official fuel economy cycle, the 330e records a 44g/km co2 rating (that can be affected by optional equipment, mind) and 148mpg. That’s 148mpg, or 2.0-litres per 100km.

Fuel economy

Okay, let’s pull the rug out slightly here. You’re not going to get 148mpg. Over a roughly 70km test route, starting with a fully-charged battery, and driving as normally as we possibly could, here’s what we managed. We squeezed 30km of electric only running out of it, which seems not bad. BMW estimates that most of its customers cover roughly 30km a day on average, so it’ll cover the average at least. Once the petrol engine kicked in, and including a mixture of motorway and urban running, we got 4.5-litres per 100km, or 62.7mpg. You could expect to get the same from a carefully driven 320d.

Having tugged the rug a little, now let’s look at pricing. Thanks to that low Co2 figure, the 330e qualifies for the full €5,000 SEAI grant and a rebate of €2,500 from Revenue on its Vehicle Registration Tax. Thanks to all that, a basic 330e SE, with standard automatic gearbox, costs €41,030 on the road. The desirable M-Sport model will set you back €45,060. The equivalent numbers for a 320d are €46,377 for an auto SE and €50,527 for an auto M-Sport. So you’re saving roughly €5k on the purchase price, paying €30 a year less in motor tax and insulating yourself against any impending diesel-power bans in city centres (which are coming, and possibly a lot sooner than you think).

This is all starting to make rather a huge amount of sense. For those of us who’s driving patterns are school runs during the week with longer journeys at weekends, you’re potentially looking at running Monday-to-Friday with zero emissions and zero fuel costs, aside from a few Euro to charge up the batteries at night. That’s a pretty tempting combo.

And the 3 Series drives much as it has ever done. Leave it all the electronic helpers in auto mode and the steering is a touch too light, but the balance and road holding remain as sharp as ever (the steering gets better in Sport mode). Aside from the smaller boot, the only real downside is that the suspension is stiffer to help control the extra weight of the batteries and electric motor (around 165kg more than a conventional internal combustion engine 3 Series) so the ride is noticeably more stiff-kneed. It’s a compromise whose nature you could probably soften by opting for softer, SE-spec springs and dampers.

2-Series is best fun yet

It’s not the most fun BMW PHEV though. That would be the 225xe Active Tourer. It uses the 1.5-litre, 136hp three-cylinder turbo petrol motor from the Mini Cooper and the same 88hp electric motor, but there’s a twist - here, the petrol engine drives the front wheels and the electric motor drives the rear wheels. So, for €42,790 on the road, you get a 225hp 2 Series, with four-wheel-drive and an automatic gearbox. That compares well with a 218d Sport 2 Series automatic, which’ll cost you €43,957 on the road and is resolutely front-wheel-drive. I’ve been, to be honest, a bit blasé about the Active Tourer so far. Nothing wrong with a front-drive BMW, but for a car aimed at families it’s a bit pricey, to say the least.

Here though, it’s just fun. Think of it as a tall-roof alternative to a conventional hot hatch (at which point the price tag doesn’t look quite so tall). The steering, also donated from the Mini, feels light, but sharper most of the time than that of the 3 Series, while in Sport spec, our test car didn’t have the ride quality issues of the saloon PHEV - firm, but not jittery. It’s also hugely enjoyable through corners (the extra down-low weight of the batteries seeming to balance the extra height of the roof) and frankly, I just didn’t want to stop driving it. A slightly worse overall fuel consumption figure (we managed 4.6-litres per 100km, or 61.4mpg against BMW’s claim of 141mpg) can be partially blamed on some excess enthusiasm on clear stretches. The only shortcoming? Again, a boot that’s a little smaller than what you get on a conventional diesel model (plus rear seats that are mounted 30mm higher, reducing headroom a little) and the fact that the electric drive can’t yet be packaged with the optional seven-seats of the longer 2 Series Gran Tourer.

Diesel killers?

It might be premature to describe either of these cars as diesel-killers, as it depends very much on how the public will perceive them and whether or not they’ll take these part-electric Beemers to their hearts in the same way that the 320d has become an acme of desirable motoring. The official figures too are something of a joke - surely no-one will ever be able to match them in day-to-day motoring, but the real-world figures we managed seem to indicate at least parity with diesel in overall running costs, with the added benefit of frequent all-electric running for those who do most of their driving downtown. Combine all that, plus the 225xe’s fun factor with the savings made on the list prices and Augsburg’s 19th century diesel efforts can, potentially, finally be consigned to the history books.

The lowdown:

BMW 330e M-Sport.

Price: €45,060 as tested; range starts at €41,030.

Power: 252hp.

Torque: 420Nm.

0-100kmh: 6.1sec.

Top speed: 225kmh.

Claimed economy: 1.9l/100km. (148mpg - see text).

CO2 emissions: 44g/km.

Motor tax: €170.

Verdict: It’s a 3 Series, but cleverer. Useful amounts of all-electric running combined with brisk performance and acceptable real-world fuel consumption. Hard ride in M-Sport spec though.

BMW 225xe Sport.

Price: €42,790 as tested; range starts at €42,790.

Power: 224hp.

Torque: 380Nm.

0-100kmh: 6.7sec.

Top speed: 202kmh.

Claimed economy: 2.0l/100km. (141mpg - see text).

CO2 emissions: 46g/km.

Motor tax: €170.

Verdict: Sensible electric running and costs, combined with huge fun factor when both motors are pulling at once. The most enjoyable PHEV yet.