A judge at the High Court has granted the Christian group Core Issues Trust permission to appeal Friday’s ruling which deemed a Transport for London ban on homophobic bus adverts lawful.

The adverts, which were due to run on 24 buses, said: “Not Gay. Ex-Gay, Post-Gay and Proud. Get over it!” and were in response to a previous bus poster campaign by gay rights charity Stonewall, which said: “Some people are gay. Get over it!”

Core Issues Trust claimed that Mayor Boris Johnson was “politically driven” when he intervened to block the adverts in May 2012, but today a judge ruled that he did not abuse his position as chairman of Transport for London (TfL) when he imposed the ban.

Mrs Justice Lang, sitting at London’s High Court, ruled that TfL’s process in introducing the ban “was procedurally unfair, in breach of its own procedures and demonstrated a failure to consider the relevant issues”.

However, she declared the ban was lawful as the posters would “cause grave offence” to the gay community and they were perceived to be homophobic.

Justice Lang did, however, give permission for the Core Issues Trust to appeal to the Court of Appeal.

Although she did not think such an appeal would succeed, she said there were “compelling reasons” to allow it to go ahead.

She said the case “concerns interference with the right to freedom of expression which is a matter of such fundamental importance that it merits consideration by the appellant court.”

Last November, Lib Dem Health Minister Norman Lamb said of gay conversion therapy: “There is no evidence that this sort of treatment is beneficial and indeed it may well cause significant harm, to some patients.”