Mini has revealed a refreshed model line-up that includes a new diesel engine which promises to dip the already ultra-popular supermini below the road tax threshold.

The brand is ditching its current oil-burner and replacing it with a BMW-built 1.6-litre four cylinder engine that emits just 99g/km CO2, making the Mini One D and Mini Cooper D exempt from taxation in the current system.

The diesel lump will be available in two power outputs. The 89bhp will be available for the hatch and Clubman only, while the more powerful 110bhp version is for all Cooper D spec models including the Convertible.

Due to their extra size and weight the Clubman and the Convertible cannot quite match the hatchback's emissions standard – they produce 103g/km and 105g/km respectively.

Nevertheless, BMW is promising frugality whichever model you choose. The manufacturer insists all versions of the diesel Mini will be capable of 70+mpg. Performance wise, the Cooper D hatch is the only variant to dip under 10 seconds for the 0-62mph sprint.

The entire Mini range will also be treated to a restrained design makeover. A new front bumper with a lower air intake that incorporates a set of fog lights is the main feature, although the Cooper S will add two additional air intakes.

The manufacturer has also gently polished the interior; updating most of the switchgear for better appearance and functionality. This being Mini there is also a range of new colours and trim options to choose from.

With the exception of the entry level Mini First, all models will now get a DAB radio as standard. The optional 6.5" widescreen sat nav has been updated, and the Mini Connected system allows iPhone users to access Twitter, Facebook and any radio station in the world with a web address.