Most BMWs feature parts of its EfficientDynamics system, but the 123d Coupé uses every aspect, which includes brake energy regeneration and auto start-stop technology.
So while the 204bhp coupé will spurt from 0-62mph in seven seconds and go on to 148mph, it will also deliver 54.3mpg (though not at the same time).
BMW is going after its youngest ever buyer profile, targeting men aged 30-40 with an income of £50,000-£70,000.
Sales are expected to reach 3,500 a year, with the entry level 120d taking 45% of the sales mix.
BMW believes the 1 Series Coupé has no rivals, but wants to poach sales from the Volvo C30, Alfa Romeo Brera and Audi S3.
However, BMW said the 135i model could tempt Audi TT and even Porsche Cayman drivers.
While it would struggle to keep up with a Cayman, the 123d is quick.
It offers 100bhp per litre and is the first four-cylinder production diesel with twin-turbo technology.
The power is progressive all the way to the red line.
The 123d Coupé’s engine will generate peak torque of 400Nm at just 2,000rpm, while peak power maxes out at 4,400rpm.
It’s refined but the gear stick suffers from the shakes and the engine note won’t satisfy performance nuts.
The 123d is crammed with technology.
The great thing about the car is that the technology doesn’t draw attention to itself.
All the systems carefully controlling the car just get on with their job and leave the driver to get on with driving.
The same can be said about the interior.
While the scarlet leather interior specified in our 123d was a bit garish, the dash was as you would expect from a German car; practical and uncomplicated.
The coupé is a lot better looking than the standard 1 Series and the 123d adds side skirts, rear diffuser and a chrome exhaust.
The BMW 1 Series Coupé uses the same underpinnings as the three and five-door 1 Series models, but has an elongated coupé body to emphasise its sportiness.
The 133mm in length over the hatch boosts the boot space to 370 litres – just big enough for the weekly shop.