Very competent and unquestionably swift, but not especially engaging. This isn't an M135i with a sensible hat on, as you might have hoped. There are obvious similarities, such as the cabin architecture and slick steering, but it lacks its big brother's verve.
In part, this is due to the engine's unexciting sound. You may bemoan the absence of artificially created engine noise but this is one instance where it would be of benefit, since beyond a rising tachometer needle there’s very little to indicate much is going on. That growling, whistling, dump valve-huffing straight six adds masses of character to the M135i, and just a fraction of that is sorely needed in the 125d M Sport. It’s a shame because it can cause you to overlook the otherwise superb four-cylinder engine which is delightfully linear in its delivery, free from lag and eager to reach its redline.
Similarly impressive are the updates to the ZF gearbox. No longer will it simply base its shifts on speed and throttle input; it will now additionally use the car's sat-nav to look at the road ahead and select and hold a suitable ratio until you've dispensed with the oncoming corner. It works well, leaving the car feeling more poised and predictable than it would have done previously. In Sport mode its shifts are remarkably quick, almost to the extent that the transmission does a convincing impression of many a mainstream dual-clutch unit.
It's also quietly gratifying to drive a diesel hatch whose front wheels are freed from transmitting the engine's power to the road. The BMW's steering is consequently uncorrupted, as well as quick to act and precise. However, while the BMW turns in with vigour and, initially, feels like a keen handler, push harder and its lustre dulls a little. For example, catch a mid-corner bump at speed with the rear wheels and you’ll feel a pronounced hop. This slightly unsettling motion cools your enthusiasm a little, and gently persuades you to take a more restrained approach. So driven, it rides and cruises in a very cosseting, relaxed fashion, which is ideal for longer trips.
Inside, it's standard 1 Series fare: smartly presented, comfortable and quiet. It’s not the best packaged hatchback but there’s seating for four adults, a decent boot and a 52-litre tank that provides a range of some 660 miles – assuming you get anywhere near the official 61.4mpg. It would have been good if BMW had knocked 1g/km of CO2 from the 125d’s emissions figure, though, as it would grant it a VED cost of just £30. Unfortunately, since it’s 121g/km, it's £110. Considering what the car offers on the performance and economy front, it’s by no means a deal breaker.