The advertising regulator has received almost 150 complaints that an atheist ad campaign, proclaiming "There is probably no God. Now stop worrying and enjoy your life", is offensive to Christians and other religions that believe in a single God.
Stephen Green, the national director of Christian Voice, is among those who have complained to the Advertising Standards Authority, arguing that the atheist campaign broke the advertising code on the grounds of substantiation and truthfulness.
The ASA has received 141 complaints about the Atheist Bus Campaign which launched earlier this week on buses throughout England, Scotland and Wales, as well as the London underground. However, 39 of the complaints are regarding newspaper and online articles about the campaign, which the ASA has no power to deal with.
The complainants claim the ad campaign is offensive to Christians and those of other monotheistic religions.
Green said: "It is given as a statement of fact and that means it must be capable of substantiation if it is not to break the rules.
"There is plenty of evidence for God, from people's personal experience, to the complexity, interdependence, beauty and design of the natural world.
"But there is scant evidence on the other side, so I think the advertisers are really going to struggle to show their claim is not an exaggeration or inaccurate, as the ASA code puts it."
The regulator has not yet decided if the complaints warrant a formal investigation to see if the campaign has broken the advertising code.
Hanne Stinson, the chief executive of the British Humanist Association, which launched the campaign, said she "pitied the ASA if they are going to be expected to rule on the probability of god's existence. However, if they do investigate we will be very happy to respond".
The campaign uses quotes from famous public figures – such as Albert Einstein, Douglas Adams, Emily Dickinson and Katharine Hepburn – who have either endorsed atheism or expressed scepticism about the concept of God.
Writer Ariane Sherine first suggested the idea in a Guardian Comment is Free blog last June, saying an atheist bus campaign would provide a reassuring counter-message to religious slogans threatening non-Christians with hell and damnation.
• To contact the MediaGuardian news desk email editor@mediatheguardian.com or phone 020 3353 3857. For all other inquiries please call the main Guardian switchboard on 020 3353 2000.
• If you are writing a comment for publication, please mark clearly "for publication".
View all comments >