Adverts which suggested gay people could be cured have been banned from London buses.
The campaign was due to run for two weeks on the side of vehicles serving five routes in the capital, including top tourist destinations such as St Paul's Cathedral, Oxford Street, Trafalgar Square and Piccadilly Circus.
The posters, by Christian group Core Issues Trust, stated: "Not gay! Post-gay, ex-gay and proud. Get over it!".
They were believed to mock pro-gay group Stonewall's recent campaign which featured adverts saying: "Some people are gay. Get over it."
But following a huge public outcry which labelled the Core Issues' campaign homophobic, London Mayor Boris Johnson, who chairs Transport for London (TfL), tonight ordered the adverts to be pulled.
Mr Johnson, who is standing for re-election next month, said: "London is one of the most tolerant cities in the world and intolerant of intolerance.
"It is clearly offensive to suggest being gay is an illness someone recovers from and I am not prepared to have that suggestion driven around London on our buses."
The campaign, which was backed by Christian group Anglican Mainstream and cleared by industry regulator the Advertising Standards Authority, claimed therapy could change sexual orientation.
It was due to run on London buses from Monday.
Core Issues' co-director Mike Davidson tonight criticised the decision to axe the adverts, saying: "I didn't realise censorship was in place.
"We went through the correct channels and we were encouraged by the bus company to go through their procedures. They okayed it and now it has been pulled.
"I would be interested to know on what basis they have done that."
He added: "It is of deep concern that there can only be one point of view and that is the point of view of individuals who are determined to push through gay marriage and apparently believe that homosexuality cannot be altered in any possible way.
"That is not a universally held view.
"This is a disturbing development and it is disappointing the UK finds itself in this position."
But Stonewall spokesman Andy Wasley welcomed the move, saying: "We are delighted by TfL's clear commitment to diversity.
"It is fantastic that no adverts will be promoting voodoo, gay-cure therapy in London."
A TfL spokeswoman said: "The adverts are not currently running on any London buses and they will not do so.
"This advertisement has just been brought to our attention by our advertising agency, CBSO, and we have decided that it should not run on London's bus or transport networks.
"We do not believe these specific ads are consistent with TfL's commitment to a tolerant and inclusive London."