Britain's Advertising Standards Authority (ASA) has upheld complaints against two of four Ryanair advertisements in the UK press, all of which invited readers to send a protest to the Treasury about then Chancellor Gordon Brown's increase in taxes on air travellers.
Complaints against two of the ads were rejected.
In one of the ads, complainants challenged a claim that 'aviation accounts for just 2% of CO2 emissions'.
The ASA concluded that this figure was based on global emissions and that the British government had calculated a figure of 5.5% for the UK.
'In the context of an ad specifically about a UK tax initiative, and which specifically referred to UK tourists, readers could interpret the 2% figure as a reference to UK CO2 emissions, not global emissions,' the ASA said.
It said Ryanair had failed to make the basis of its 2% claim sufficiently clear.
The second complaint upheld concerned an ad which claimed that 'not a penny' of the money collected in the tax would be spent on the environment.
The ASA said Ryanair had not provided sufficient evidence to prove this.
In response, Ryanair criticised the ASA and said it would continue to use these 'factually accurate' statements in its advertising.
The ASA rejected complaints about an ad which said 'UK tourists will pay £1 billion more in taxes', while it also said an ad using the image of the Pope 'was unlikely to cause serious or widespread offence'.
