The results (available online here) come from a test procedure established with two non-governmental organisations, Transport & Environment (T&E) and France Nature Environment (FNE) and follow the publication earlier this year of the carmaker’s first real-world economy tests, which were carried out on three of its cars.

The new fuel economy data is based on the European Union's Real Driving Emissions (RDE) project, with the procedure measuring fuel consumption by means of a portable emissions measurement system (PEMS) installed on the vehicle. The results are audited by Bureau Veritas.

Models covered include the 308 1.6l BlueHDi 120 S&S BVM6, which has an official fuel economy figure of 3.2l/100km but achieved a figure of 4.9l/100km in the real-world test.

The Citroën models tested include the C4 BlueHDi 100 BVM Feel, which has an official fuel economy figure of 3.6l/100km but achieved 5.1l/100km.

The DS 3 and 4 were also tested, with the DS 4 PureTech 110 S&S BVM So Chic achieving 5.4l/100km in the real world test compared to 3.8l/100km for its official result.

Greg Archer, clean vehicles director at Transport & Environment, said: “This real-world test provides more representative information to consumers than new laboratory tests, helping them to choose the most fuel-efficient, low-carbon models.”

The group will publish figures for another 20 models by the end of the year and introduce a simulator allowing customers to reduce their fuel consumption depending on driving conditions.

Next year, PSA will add in measurements to cover nitrogen oxides (NOx) in customer driving conditions.