The model – Citroen’s first production hybrid – has been given a software-related upgrade that sees emissions for the entry-level DSign trim model drop from its current lowest level of 91g/km to 88g/km with its standard 17-inch alloys.

The higher-spec DStyle and DSport models can also be downgraded to the 17-inch alloys at no extra cost, giving them a CO2 emissions figure of 88g/km compared with 102g/km for the standard models. This ensures that both models now qualify for 100% exemption from the London Congestion Charge and VED road tax as well as a reduction in BiK from 11% to 10% for 2012/13.

The latest changes to the energy regeneration system follow the introduction late last year of new battery management software that saw emissions fall from 99g/km to 91g/km for the DSign and from 107g/km to 102g/km for the DStyle and DSport models on their standard wheels.

The newest model in Citroen’s DS line-up, the DS5 flagship crossover went on sale in April last year and sits above the firm’s DS3 and DS4 models. The Hybrid4 combines a 163bhp 2.0-litre HDi engine driving the front wheels with a 37bhp electric motor powering the rears, giving a total output of 200bhp and a 0-62mph time of 8.3 seconds.

Prices for the Citroen DS5 Hybrid4 line-up remain unchanged, starting at £27,600 for the DSign Hybrid4 200 Airdream EGS6.