If you want a BMW 1-Series in your life, there are plenty to choose from. I make it that there are 108 individual models in the line-up, and even if I've dropped a stitch somewhere along the way that's still a heck of a lot of small BMWs.Of these 108, or whatever it is, two are of particular interest if low running costs are a priority. These are the three- and five-door versions of the 116d EfficientDynamics, and what sets them apart from other 1-Series models is that they're the only ones with official double-figure CO2 emissions.This means (all together, class) that they're exempt from both Vehicle Excise Duty and the London congestion charge. The second of these advantages is of course significant only to people who live outside the charge zone and have to drive into it. For everyone else, the saving over a car which emits 101g/km amounts to just £20 annually from year two onwards.The EfficientDynamics is unusual among 116ds in that it has a 1.6-litre diesel engine. All the others have two-litre diesels, though the two units perform in incredibly similar ways. BMW quotes exactly the same maximum power and torque figures, at exactly the same engine speeds, for both.As you can imagine, straightline performance is almost indistinguishable - the EfficientDynamics is very slightly slower than a two-litre 116d with manual transmission and very slightly quicker than an automatic. The difference in CO2 emissions is substantial, though, and the 74.3mpg official combined fuel economy is 11.5mpg better than that of the two-litre cars.(Whether or not you'll manage 74.3mpg yourself is another matter. I imagine it would take a lot of concentration, though this test wasn't long enough for me to find out.)Although the high rear sill doesn't make loading as easy as it could be, the 1-Series has a decently large boot. Luggage capacity with the rear seats in place is 360 litres - not so much as in the new Volkswagen Golf but more than in a Vauxhall Astra and much more than in a Ford Focus.Rear passenger room isn't nearly as impressive. At six foot three, I couldn't sit in the back at all unless someone very short was sitting in front of me.On the road, the fact that the 1-Series is the only rear-wheel drive car in its class means that it feels quite different from all its rivals. Personally, I've never had a problem with front-wheel drive, but it's nice not to feel the effects of what the engine is doing come through the steering wheel.The gearchange is above averagely good for a BMW (not a company famed for getting this right on every occasion) and the ride is remarkably smooth. If anything, the suspension set-up is slightly too soft, the result being that the body of the car hardly ever seems to be at rest except on the very finest road surfaces.Another positive feature is the low level of engine noise. At a 70mph cruise in top gear the 1.6 diesel is puttering along at just 1800rpm and is effectively inaudible.Perhaps surprisingly, the current list price is under £21,000, which seems rather good. But this is a BMW, and as usual there are more than enough opportunities to continue spending money - the test car, for example, had no less than £6580 worth of options. Engine 1598cc, 4 cylinders Power 116bhp Transmission 6-speed manual Fuel/CO2 74.3mpg / 99g/km Acceleration 0-62mph: 10.5 seconds Top speed 121mph Price £20,885 Details correct at publication date