Sector: Large SUV Price: £45,380 Fuel: 44.8mpg CO2: 165g/km

Built largely to meet the tastes of the SUV-loving American market, the gargantuan Mercedes-Benz ML has never really been a front-runner in the economy stakes. But where old models used V6 and V8 engines, the third generation has become the first to feature a four-cylinder diesel in the ML 250 BlueTEC.

As the name implies, it’s the same 2.1-litre, 201bhp unit found in almost every model the carmaker sells. Not a bad thing, either. It’s a smooth, silent and powerful engine that works well in everything from the SLK to the E-Class, and makes the predominantly fleet-bought ML a more tax-conscious option.

Even so, moving 2.2 tonnes of ML with a four-cylinder diesel engine sounds like a tall order. Not only does it have to offer the refinement usually accompanied by the three-pointed star, but big SUVs tend to carry large loads, and even models such as this are used for towing and some light off-roading.

This is just about up to the task. The engine is less refined than the V6, but not significantly so, and it’s quite happy to haul the large and unaerodynamic body around. While it’s by no means a performance car, feeling a little sluggish off the mark, it still can tow up to 2,950kg and doesn’t feel like it’s suffering at high speed.

Against the sharper-driving Audi, BMW and Porsche models with which this shares a segment, Mercedes-Benz has tried hard to tighten up the way the ML takes care of corners. Aside from the sheer size, this is very manoeuvrable with a tight turning circle and impressive stability for something so tall. The non-adaptive sports suspension does tend to make the car lurch about on bumpy roads, though.

It’s not faultless. Like most car manufacturers, Mercedes-Benz is resorting to downsizing to cut emissions and boost efficiency, but there’s a limit. While the ML 250 doesn’t feel underpowered, the engine is permanently working hard to move the large body, which in turn puts a void between the 44.8mpg claimed efficiency and 31mpg achieved while on test.  

The ML 350 BlueTEC may be more efficient on paper, but by working less hard on the road it’ll probably come closer to the claimed 39.2mpg. It’s the right engine for the car.

Ultimately it depends what you’re after. The ML 250 BlueTEC is still relatively efficient for a large SUV, and doesn’t feel as sluggish as downsizing drivers may expect. But it’s a car for those seeking a tax-efficient route to ML ownership, rather than one which will offer massive frugality.

Verdict:

The ML 250 BlueTEC sacrifices little in its push for low CO2 emissions, retaining most of its relaxed cruising ability and towing capacity. But the small engine is being worked too hard here, which means outside the NEDC test cycle the most frugal ML to date may not offer as much of an advantage as claimed.