What is it? This is an even more efficient version of the diesel A1 supermini. By tweaking the 103bhp 1.6-litre engine, Audi has managed to boost fuel economy from 70.6mpg to 74.3mpg.
At the same time, CO2 emissions fall from 105g/km to 99g/km, making the car exempt from the London congestion charge, and also from road tax.
As before, the diesel model is available in all three A1 trims. Our test car was a range-topping S line, the first time we've driven a diesel A1 in this form.
From the outside, S line models can be identified by their 17-inch alloy wheels, S line rear spoiler and sports bumpers, while inside they have part-leather upholstery and aluminium door sill inlays.
The other notable element of S line trim is the standard sports suspension.
What's it like to drive? While the stop-start system allows moments of peace, the diesel engine is loud enough to disrupt the A1's otherwise serene cabin.
Fortunately, the diesel engine offers plenty of zip for town driving and decent flexibility at higher speeds.
The A1's handling is fun, with the body control and steering set-up delivering the solid feel of a much larger car.
That said, S line suspension is too stiff for a car that is aiming at frugality first and foremost. We prefer the slightly softer-riding SE and Sport models.
What's it like inside? S line trim makes for an attractive interior, with the badging on the door sills and dashboard a particular highlight. Otherwise it is standard A1 fare. This means a well-finished, solid and nicely styled dashboard that features user-friendly controls.
The part-leather seats bring a touch of luxury to the supermini class and go a little way to justifying the S line's high price .
As in other A1s, there's plenty of space up front, but the dramatically sloping roofline means the rear seats are best left to children.
Should I buy one? While the diesel engine is the most efficient in the A1 range, the petrol models aren't that far behind. Given the premium you pay for the diesel on the purchase price and on company car tax, you'd have to do a lot of miles to see the rewards.
Still, the fact that Audi has managed to get emissions below 100g/km is impressive, and to do so without compromising the A1's looks and driving ability is even more so. Just be sure to avoid the expensive and firm-riding S line model if you choose the diesel.
What Car? says