A Christian group was at the High Court yesterday to challenge London Mayor Boris Johnson's decision to ban their gay bus ad.

The Core Issues Trust booked an advertising campaign on London buses carrying the slogan: "Not Gay! Ex Gay, Post Gay and Proud. Get over it!"

The bus ad was intended as a call for respect towards individuals who have experienced same-sex attraction but would not describe themselves as gay but rather "ex-gay" or "post-gay".

The Core Issues Trust had wanted to run the advert on London buses in response to a previous advertising campaign by gay lobby group Stonewall, which featured the slogan "Some people are gay. Get over it!" 

The Stonewall advert was approved by Boris Johnson, but he refused to give the go ahead to the Core Issues Trust advert on the grounds that it would cause "offence" to homosexuals and possibly result in violence against the Christian community.

Core Issues Trust director Dr Mike Davidson, who is ex-homosexual, was seeking a reversal on the ban at the High Court on Thursday.  

He argued that the Mayor's actions had unlawfully restricted free speech and discriminated against the trust by only allowing one side of the debate to air its views.

Dr Davidson pointed out that Transport for London runs other controversial adverts, including those for abortion services and a recent campaign by the British Humanist Association carrying the slogan "There's probably no God. Now stop worrying and enjoy your life". 

"This is all about being free to talk about these issues, and the right of individuals to take a sexual identity that is consistent with other values in their lives. Those individuals who are post-gay or ex-gay are a sexual minority suffering discrimination because they are outside the purportedly 'normative' homosexual paradigm," he said.

"It was a mistake to assume these views we were expressing came from entrenched homophobia, and failed to recognise that people who want to walk away from their homosexual feelings are a group in their own right."

Andrea Williams, Director of the Christian Legal Centre, which is supporting Dr Davidson's case, said: "In a truly democratic society people should be free to choose to change their behaviour and move away from homosexual behaviour if they wish.

"The possibility that a section of the public will take 'offence' to a particular viewpoint is not a legitimate ground for restricting freedom of expression. The concept is simply being used by the State to censor opposing views and obliterate debate in the public sphere.

"Boris Johnson needs to realise his mistake and ensure there is freedom for all in the marketplace of ideas. He cannot prefer one group over another."