It's not often you get to start a piece on a new car with such a bald question, but what is the BMW 1-Series actually for? Yes, it's sold over a million units since it arrived in 2005, so somebody out there obviously likes it. On the other hand, with the best will in the world, it's always been a bit of an ugly spud, with a compromised profile and wonky detailing (brilliantly chunky 1 M Coupe apart). While we clearly approve of its rear-drive set-up for dynamic reasons, we're also rather attached to our legs, and no amount of bribery would induce anyone of above-average height to sit in the back of a 1-Series for longer than was strictly necessary.
This all-new model addresses some of these fundamental problems, while taking BMW's laudable drive for efficiency to impressive new levels. Let's start with some numbers. The new car is 85mm longer than the old one, its wheelbase has grown by 30mm - most of which is donated to the cause of rear legroom - and the front and rear track have also been widened. Boot capacity is 30 litres bigger, too.
Few cars these days, it seems, are immune from dimensional inflation, but in the 1's case that's no bad thing (maybe there'll be a BMW 0.5-Series before long). Despite all this expansion, it's 30kg lighter than before, and its torsional rigidity is improved by almost a third. It's not a whole lot better-looking, though. Now I'm a champion of the different, and a bigger fan of BMW's complex design language than most of my Top Gear colleagues. The latest 5-Series, for example, is a toweringly good piece of work. But the new 1 looks to the 5-Series GT for visual inspiration instead, which is a bit like asking Chitty Chitty Bang Bang's child-catcher for parenting tips. Bigger lights, enlarged forward-leaning double kidney grille, three-section air intake, with four distinct contour lines to add some visual tension: it's all going on, but rather than looking sporty, the new 1 merely looks like a car that's just discovered that its phone's been hacked. There's some clever sculpture on the body-sides, but quite simply the current Golf GTI is better-looking.
Anyway. The technology's the thing here. Exclusively turbocharged (TwinPower in BMW parlance), the 1 lands in the UK next month with a choice of five engines: 135 or 168bhp direct injection, twin-scroll turboed 116i or 118i petrols, and no fewer than three 2.0-litre common-rail diesels, in 116, 143 or 184bhp degrees of, if not hotness exactly, then tepidity.
You could probably write a thesis on EfficientDynamics, but in the new 1-Series let's just say that BMW's eco-tech manifesto may have come of age. An ultra-green 116d ED is coming soon, with claimed CO2 emissions of 99g/km and a combined average of 74mpg, but even the pokiest 120d serves up a decent slab of cake and invites you to eat it. Apparently, it'll do 60mph in just over seven seconds and tops out at 140mph, but emits just 119g/km, and - provided your right foot isn't permanently made of lead - should average around 60mpg.
That's on paper. Time to hit the road. BMW's smallest car now has a cabin that's on a par with its much bigger, pricier siblings. It's almost a decade since iDrive appeared in its brave but misfiring v1.0 incarnation, and, for my money, BMW's current multi-media system is easily the most elegant and user-friendly of the lot. Hard drive-based navigation and 12-speaker Harman/Kardon hi-fi with DAB and a digital amplifier are all brilliant if pricey options, but even a parched 1-Series is a handsome place to be. Good materials, great driving position and some decent design flourishes. I love the interior doorhandles, and the cup-holder recesses in the base of the doors are cleverly designed and spacious. Here, at least, it kicks a Golf or A3 into touch.
It gets better. As with the previous 1, this might be a small BMW, but the bits underneath are very grown-up. The suspension is independent all-round, with MacPherson struts on the front and a sophisticated five-link axle at the rear. The front axle is mostly aluminium, which reduces unsprung mass, and the suspension's kinematics have all been sharpened. You can tell immediately. A veteran of numerous ruinously run-flat-clad BMWs, I actually got out after 10 minutes to double-check that TG's test car was actually on them and that my arse wasn't lying to me. It's still firm enough, don't get me wrong, but it filters out the worst that the UK's beaten roads can chuck at it while maintaining a decent entertainment focus.
The new car also features a ‘driving experience switch' as standard, allowing you to flick between Comfort, Sport or Eco Pro, each remapping the engine, tweaking the DSC threshold and altering the shift points of the ZF eight-speed automatic (an option, but it's such a good transmission we'd recommend it). There's also an optional adaptive suspension, which is 10mm lower than the regularly sprung car, but the message here is of ‘enhanced comfort' above all else. So don't bother with it. That said, die-hard BMW fans will be pleased to hear that this small diesel hatchback will go sideways with little provocation, if that's your bag. Everyone else will enjoy an electro-mechanical steering rack that guarantees pleasing fluidity and body control that rewards what whiskery old road-testers used to call ‘press-on' driving.
I like this car a lot. Everyone still bangs on about BMW's peerless driving dynamics, but the fact is that the Munich legend means something different these days. The 120d is one of the most energetic diesels I've ever driven, its auto 'box is terrific, and it's so clean I'd dearly like to drive it into eco-man George Monbiot's Toyota Prius. So that's what it's for.
We like: It's fast, fun and clean
We don't like: It still looks a bit funny
The verdict: Not gut-punchingly desirable, but now more rational than ever.
Performance: 0-62mph in 7.2secs, max 142mph, 62.7mpg
Tech: 1995cc, 4cyl, RWD, 184bhp, 280lb ft, 1420kg, 119g/km CO2
Tick this on the options list: H/K stereo & DAB digital radio, £875
And avoid this: rear-seat: iPad dock, £tbc