The Core Issues Trust has lost its appeal against a decision to ban an advert on London buses, and ordered to pay £100,000 in costs to Transport for London.

In April 2012, Core Issues Trust tried unsuccessfully to advertise anti-gay posters on 24 London buses in a direct response to Stonewall’s pro-gay posters.

The Trust’s posters read: “Not Gay. Ex-Gay, Post-Gay and Proud. Get over it!”

Although the ad campaign was passed by the Committee of Advertising Practice, Mayor of London Boris Johnson instructed Transport for London to pull the campaign before it could run – just days before the 2012 Mayoral Election.

The Trust accused Mr Johnson of unlawfully using his position as chairman of TfL to obtain the ban in order to secure the “gay vote” and advance his 2012 re-election campaign.

In 2013, the High Court ruled that the ban was lawful, as the advert would “cause grave offence” to those who were gay, and was perceived as homophobic, “thus increasing the risk of prejudice and homophobic attacks”.

Core Issues Trust have been refused a further appeal by Lord Justice Sullivan, who said the ban was “certainly not unlawful”.

Andrea Williams of the Christian Legal Centre said they would keep fighting. She said: “This is intimidation. It is an extortionate amount of costs against somebody seeking to do good.”