Fiat has become the latest firm to have its wrist slapped over a misleading green advert, after the Advertising Standards Authority ruled two adverts earlier this year gave the impression that the company's low emission vehicles were cheaper than they are.

The press adverts for four different models of Fiat cars claimed that they would be exempt from the congestion charge from October and that they required road tax of just £35 a year.

However, the headline prices for the four models in question – Fiat Bravo, Grande Punto, 500 and Panda – were for bottom of the range models.

Consequently, the ASA ruled "that three of the four headline prices featured next to the images were for models that had higher CO2 emissions figures" than the 120g/km required to qualify for exemption from the congestion charge and the £35 road tax band.

It ruled that the adverts could mislead, and welcomed Fiat's assurance that the adverts would not be shown again.

The ruling further highlights the close scrutiny green themed adverts are facing from the public and the ASA.

The watchdog said in its annual report that complaints over environmental claims increased more than five fold last year, a trend it expects to continue this year.