BMW is to complete the engine line-up for the 1 Series five-door hatchback, with three new powerplants arriving within months.

The 116d EfficientDynamics will be BMW's most efficient model ever, dipping to the magic 99g/km marker and achieving 74.3mpg in EU tests. The engine is a 1.6-litre turbodiesel that allows the car to reach 62mph in 10.5 seconds.

All the stops have been pulled out to make the new 116d EfficientDynamics as frugal as possible. Low rolling resistance tyres, taller gearing and lower suspension are employed, along with a centrifugal pendulum that certainly sounds impressive even if its function is a mystery.

The bottom line is that the newest 116d is free of road tax and escapes the London congestion charge. It also achieves the lowest benefit-in-kind rate of 13%. It will be priced from £20,885.

Towards the other end of the scale, the 125d and 125i are only available in M Sport trim - a new addition to the five-door hatchback range. They both feature the same power, at 215bhp, and identical 6.5-second 0-62mph acceleration times.

That's where the similarities end, however, with the diesel 125d offering much more torque and a claimed 57.6mpg thanks to its twin-turbo engine, which features one small and one large turbocharger in sync to ensure quick throttle response and high performance. CO2 emissions will stand at 129g/km.

The petrol 125i will be more costly to run, at 44.1mpg and 152g/km of CO2, but it will be much cheaper to buy. It should also offer a purer driving experience for enthusiasts thanks to a higher-revving nature with a single, twin-scroll turbo.

At £26,030 the 125i will be £1,790 cheaper than the £27,820 125d.