The groups behind the ‘ex-gay’ London bus adverts which were banned last night are reportedly instructing lawyers to sue the Mayor of London and advertising display agency CSBO.

Anglican Mainstream and the Core Issues Trust had booked space on 26 London buses for an advert which read ‘Not gay! Ex-gay, post-gay and proud. Get over it!’ in a direct response to Stonewall’s ‘Some people are gay. Get over it!’ campaign.

Both groups advocate therapy to turn gay people straight, a practice condemned by professional bodies.

The Independent reports exclusively today that they have instructed Manchester lawyers Aughton Ainsworth to represent them in a legal challenge of the advert ban.

PinkNews.co.uk carried a story early yesterday afternoon on the planned adverts which was followed by stories in the mainstream media prompting an eruption of criticism across the capital and the country leading the Mayor of London to intervene and ban the advertisements.

MayorWatch reported that Transport for London said the responsibility for approving the advertisement rested with display ad agency CBSO and that CBSO had used TFL policy to decide on whether to approve the message. TFL said it “reserve[s] the right to overrule them if we do not agree with their interpretation as in this case.”

Announcing that the adverts would not go ahead, Boris Johnson said of the campaign: “London is one of the most tolerant cities in the world and intolerant of intolerance. It is clearly offensive to suggest that being gay is an illness that someone recovers from and I am not prepared to have that suggestion driven around London on our buses.”

Stonewall said it was “delighted by TfL’s clear commitment to diversity”.

The Independent records today that Aughton Ainsworth will examine two possible legal challenges: breaches both of contract and of the groups’ human rights to freedom of conscience and freedom of expression.

David Pink, the UK Council for Psychotherapy’s Chief Executive said today: “We are shocked that despite their continued claims to be a tolerant organisation, Core Issues Trust seem to think it’s better to spend money on a bus advertising campaign that reinforces the type of messages that lead to homophobic attitudes in the community.

“As the leading professional psychotherapy organisation, we are absolutely committed to our members providing a safe space for individuals to explore their sexuality.

“We utterly condemn professionals who practice ‘reparative therapy’ as sexuality is not a symptom which needs treating or correcting.”

The Royal College of Psychiatrists “believes strongly in evidence-based treatment. There is no sound scientific evidence that sexual orientation can be changed. Furthermore, so-called treatments of homosexuality create a setting in which prejudice and discrimination flourish.”