The ad, which appeared in The Independent, was headlined 'In The Name of The Father' and featured The Holy Bible next to a pool of blood.
The GPA said the campaign was designed to draw attention to a reported 74% rise in homophobic incidents in the last year, where the main factor was the religious belief of the perpetrator.
The text of the ad read: "In the last 12 months, the Gay Police Association has recorded a 74% increase in homophobic incidents, where the sole or primary motivating factor was the religious belief of the perpetrator."
The GPA maintain that the ad, which was devised to coincide with the 2006 Euro-Pride event, was intended to be "thought-provoking and challenging", and argued that the accompanying text, "made clear the issues referred to were not exclusive to Christianity".
However, a series of complaints by Christian groups, including Christian Watch and The Evangelical Alliance, accused the GPA of acting irresponsibly for singling out Christians for "vilification and discriminatory stereotyping".
The ASA ruled that the ad breached its decency clause 5.1, stating: "The leading implication of the ad was that Christians were the perpetrators of the reported incidents.
"Because of that implication, we considered it likely that the ad would cause offence to those readers who were Christian."
Further complaints that the ad implied that "all reported incidents [of homophobia] involved physical injury", and that the GPA had not submitted evidence to substantiate its 74% rise claim, were also upheld.
The ASA told the GPA to ensure future campaigns were not presented in the same way and to substantiate its statistics.
The GPA said it had written to the complainants, apologising for any offence caused and confirmed it would desist from running the ads in the future.
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