Citroen has accused the Government of ‘moving the goal posts’ with its rules on which vehicles can be exempt from the London congestion charge.

Citroen’s C2 and C3 ‘Stop and Start’, which minimise exhaust gases by switching off their engine when stationary, is not exempt from the congestion charge, in the same way as other vehicles with low fuel consumption like the Toyota Prius.

However, the Energy Saving Trust (EST), which decides which cars must pay the congestion charge, admitted the C2 met required criteria because of its low carbon dioxide emissions and good fuel economy.

A letter sent from the EST to Citroen said: "The vehicle meets the emissions requirements, yet we believe the issue of cleaner/alternative fuels is the key principle.

"Transport for London has agreed with this position and has said the discount should only be offered for alternatively fuelled vehicles. Exempting other types of vehicles would go against the spirit of the scheme."

In the letter, both the EST and TfL both admitted the system 'wasn't perfect' and 'is in need of revision'. Citroen managing director, Xavier Duchemin, has written to Ken Livingstone, asking him to reconsider the decision.

A Citroen insider, said: "We're very disappointed with this decision, but we will hit back with innovative incentive schemes like offering a discount off the list prices of C2 and C3 stop and start models."

Citroen will be offering to pay the equivalent of 212 days worth of the £8 congestion charge (£1,696) to all C2 and C3 stop and start customers across the UK from April 3 until June.

Transport for London is currently considering changes to the congestion charge exemption rules.

Citroen will be advertising its 48 sheet congestion charge campaign around the M25 area