A new legal action has been launched against carmakers over the claimed fuel economy performance of their cars.

Italian consumer group Altroconsumo has filed a writ of summons against Fiat Chrysler Automobiles and Volkswagen after it carried out an investigation which it claimed showed consumers were being misinformed by advertised fuel efficiency information.

Its tests found two models, the Fiat Panda 1.2 and Volkswagen Golf 1.6TDI, consumed 20% to 50% more fuel than advertised, reports the Financial Times.

This latest action comes after Hyundai and Kia agreed with US regulators to pay $300m in fines for overstating fuel economy statistics last year, and BMW also revised down fuel efficiency claims for some Mini cars offered in the USA.

Advertised fuel economy figures are those from the official EU testing regime, the New European Driving Cycle which was introduced in the 1970s, however it is widely recognised that it does not reflect real world driving patterns today.

The EU is aiming to bring in a tougher test, the World Light Vehicle Test Procedure, by 2017. However, BMW chief executive Norbert Reithofer last year said the industry was lobbying to push this back to 2020.

ACEA, the European carmakers trade body, said of the WLVTP: "Industry certainly welcomes the WLTP as it will provide more robust figures for comparing one vehicle against another in terms of their CO2 emissions and fuel economy. 

"However, ACEA underlines that the new WLTP needs to be completed properly without rushing to meet unrealistic deadlines - so that it is robust and can apply to all vehicle technologies in a manufacturers’ portfolio."