Budget airline Ryanair has been warned not to understate the aviation industry's contribution towards global CO2 emissions.
The warning comes after Britain's advertising watchdog upheld 34 complaints over a national press advert claiming that aviation accounted for two per cent of total CO2 emissions.
The Advertising Standards Authority (ASA) has also rapped the no-frills carrier over a separate press ad that belittled the government's commitment to combating climate change.
In the first offending advert, the then chancellor Gordon Brown's head features on a cartoon robber's body (complete with 'swag bag') with the headline 'the great plane robber'.
An accompanying caption reads: "Gordon Brown has doubled air passenger duty on passengers to £10. He claims this is for the environment this claim is rubbish. Aviation accounts for just two per cent of CO2 emissions. This year greedy Gordon will nick £1 billion from passengers."
In its defence Ryanair claimed that the UN itself had said the aviation industry contributed two per cent of global greenhouse gas emissions and that it regarded this as "sufficient to substantiate the claim in the ad".
But the ASA ruled that the advert was misleading, especially given the insistence in Mr Brown's pre-budget report that aviation firms were responsible for 5.5 per cent of Britain's CO2 emissions.
"We considered that, because Ryanair had failed to make the basis of the two per cent figure quoted in the ad sufficiently clear, it was likely to mislead," a statement said.
The ASA says that Ryanair has been told not to repeat its claims on carbon emissions and the government's lack of redistribution of air passenger duty on climate-change initiatives.
However, the ad watchdog did not uphold complaints on two separate press adverts that featured a cartoon Mr Brown meeting the Pope and winning an Oscar for "best stick-up".