City car brand Smart will have the lowest-emission conventional-engined car on sale in the UK from early next year.

A diesel CDI version of the two-seater Fortwo coupe and cabriolet is being readied in right-hand drive guise for the first time, offering an incredible 85.6mpg and just 88g/km of CO2.

The tiny 45PS 799cc three-cylinder common-rail direct-injection engine won’t be the quickest on the road but still manages to scrape under the sub-20 second 0-62mph barrier, recording 19.8 seconds for its ‘sprint’. Top speed will be 84mph.

Sales start in February 2009 with prices likely to be slightly higher than the petrol equivalent – if pricing in continental Europe is any guide – and expected to start from circa £7500 in Pure and Passion trims only.

Due to launch sooner – in October 2008 – all petrol Smart Fortwo coupe and cabriolet models become stop/start technology-enabled as standard offering 65.7mpg and 105g/km CO2.

Marc Palmer, UK product manager for Smart, reported strong sales for the Smart this year, with 2000 registrations recorded in the first quarter and sales of about 500 a month at present – 20-30% of which are going to business customers.