A Gay Police Association (GPA) advert which linked a rise in homophobic attacks to religious belief breached advertising rules.
The advert appeared ahead of the Europride parade
The advert showing a Bible and a pool of blood led to 553 complaints to the Advertising Standards Authority (ASA).
The watchdog said there was an implication, without evidence, that Christians were the main cause of homophobic incidents.
The GPA said the press campaign was meant to be thought provoking.
Christian Watch, the Fellowship of Independent Evangelical Churches and the Trinitarian Bible Society found the advert "offensive and derogatory".
Others complained the image of blood misleadingly implied all incidents were violent and questioned whether the GPA could prove that religious beliefs had caused the rise in homophobic crimes.
The advert appeared in the Diversity supplement of the Independent newspaper on 29 June, two days ahead of the Europride gay and lesbian parade in London.
It stated: "In the last 12 months, the GPA has recorded a 74% increase in homophobic incidents, where the sole or primary motivating factor was the religious belief of the perpetrator."
An ASA spokeswoman said: "This is our most complained about campaign advert of the year so far. People thought it was portraying Christians in a bad light."
The GPA said the majority of the 250 calls relating to homophobic incidents its helpline received in the year up to March 2006 were "weighted against Christianity" while 25 referred to Islam.
The GPA was formed in 1990 and has members in all 52 UK police forces.