National advertising by two campaign groups opposed to UK airport expansion was misleading and should not be repeated, the Advertising Standards Authority has ruled.

The advert featured a photograph of premier Gordon Brown and urged the public to send a copy of it to Downing Street in protest. It was placed by AirportWatch and enoughsenough.org.

The ASA said the advert breached two elements of the Code of Advertising Practice – truthfulness and substantiation – by  misrepresenting results of an ICM poll, claiming it proved 60% of the public were opposed to airport expansion due to its impact on climate change.

The ad was also deemed “likely to mislead” because it quoted figures for aviation emissions based on the ­campaigners’ own calculations, rather than official data.

The ruling, which followed a complaint by easyJet and a member of the public, was welcomed by campaign group ­Future Heathrow, whose members include IATA, BAA, British Airways and Virgin Atlantic.

Commenting on the decision, Future Heathrow campaign director Clive Soley said:  “The adjudication is very serious. It shows that these groups, which represent some of the most vocal campaigning organisations against plans for Heathrow’s sustainable expansion, have used polls and data to mislead the public.”