Mercedes has added new low-emission A-class and B-class models to their line-up with CO2 now starting from 92g/km.

Badged Eco SE, the A180 CDI is capable of 78.5mpg. The previous best for the range was 74.3mpg. The B180 CDI Eco SE has emissions of 98g/km and an official fuel figure of 74.3mpg, an 8% efficiency improvement.

The gains for the cars come from weight reductions as well as aerodynamic improvements including a reduction in ride height. The A180 CDI Eco SE is priced from £21,965 and the B180 CDI Eco SE costs from £22,950.

Meanwhile, Mercedes is also adding the option of four-wheel drive to the A- and B-class ranges from January 2014. The A250 4Matic is available from £28,985 and the B220 CDI 4Matic starts at £28,135.