The warning comes after car manufacturers have recently advertised new cars, which claim to have improved pollution figures and lower CO2 levels, but in fact have embellished claims and contravened advertising guidelines.

The ASA is now raising consumer awareness of misleading ads and reminding advertisers of the rules and why it is not easy advertising being green.

“Advertisers have every right to promote their green credential and many have been quick to reassure consumers about the efforts they are making to be greener,” said ASA director general Christopher Graham.

“However, the ASA needs to see robust evidence to back up any eco-friendly claims. We will continue to ensure that the public are not misled and that advertisers are operating in a climate of truth.”