LONDON—London transport bosses on Thursday banned an advert that was due to be displayed on the side of its famous red buses which suggested that therapy could stop people from being gay.

Christian group Core Issues Trust said Transport for London (TfL) was guilty of censorship after it pulled the plug on an advertising campaign that appeared to mimic an ongoing initiative by pro-gay group Stonewall.

A TfL spokesman confirmed the adverts would not be seen on London’s roads, explaining it did not reflect the capital’s “tolerant and inclusive” ethos.

Some 1,000 London buses currently carry the slogan “Some people are gay. Get over it!” as part of Stonewall’s campaign, which was launched on April 1.

In the counter-campaign, posters carrying the phrase “Not gay! Post-gay, ex-gay and proud. Get over it!” were due to be displayed on London’s buses from next week.

London mayor Boris Johnson backed the ban, saying: “It is clearly offensive to suggest that being gay is an illness that someone recovers from and I am not prepared to have that suggestion driven around London on our buses.”

However, Core Issues co-director Mike Davidson maintained the group had met TfL’s requirements.

“We went through the correct channels and we were encouraged by the bus company to go through their procedures,” he said. “They okayed it and now it has been pulled.”