Pinknews.co.uk reports that religious groups were to run the campaign which claimed “gay people can become straight.”
The ads were a response to gay rights group Stonewall’s current advertising campaign in favour of gay equality.
Mayoral hopeful Brian Paddick and Ken Livingstone condemned the adverts following the Pinknews.co.uk report.
Mr Paddick said: “From personal experience as a gay Christian, I can tell you that it’s much better to be out than in. We should be celebrating the diversity for which London is known for, not denegrating it.”
Ken Livingstone claimed the decision to accept the ads prived “London is going backwards under a Tory leadership that should have made these advertisements impossible.”
Transport for London later announced it had banned the ads and a spokesman attempted to distance the body from the campaign, insisting responsibility for approving it rested with display ad agency CBSO.
The spokesman said it was CBSO who approved the ad “using our Ad Policy” but said TfL “reserve the right to overrule them if we do not agree with their interpretation as in this case.”