A bus poster which read: "There definitely is a God" attracted more complaints than any other advert in 2009, the Advertising Standards Authority said today.
A total of 1,204 people complained that the Christian Party ad was offensive to atheists and could not be substantiated.
The ASA did not investigate the ad - a response to a British Humanist Association (BHA) poster reading: "There is probably no God. Now stop worrying and enjoy your life" - because political party campaigns are outside its remit.
The ASA also did not investigate the BHA ad, which was the sixth most complained-about campaign with 392 objections, concluding that it was an expression of the advertiser's opinion and not capable of being objectively substantiated.
BHA chief executive Andrew Copson said: "Our adverts were a light-hearted response to exactly the kind of dogma that says people must be told what to believe and how to live, often accompanied by the threat of punishment in another world.
"It is with some satisfaction that the public chose to complain about an advert that did not want them to decide for themselves about the existence of god, rather than encouraging them to make their own minds up as ours did."
The total number of complaints to the ASA increased by 9.6% to 28,978, although the number of ads attracting complaints declined by 10% to 13,956.
ASA rulings led to 2,397 ads or campaigns being changed or withdrawn.
Volkswagen produced the second most complained about ad, with 1,070 objections, for including graphic scenes of a man fighting his clones. The ASA partly upheld the complaints.
HomePride took third place with 804 complaints for an oven cleaner ad reading: "So easy, even a man can do it". The ASA ruled that the ad was tongue-in-cheek and did not uphold the complaints that it was offensive.