A Christian campaign group is threatening to take legal action against the government if it goes ahead with a ban on so-called conversion therapy.
Christian Concern said that the proposed ban raises "serious questions" about religious freedom, and risks infringing on individual freedoms and breaching the European Convention of Human Rights.
A legal opinion from Christian Legal Centre lawyer Roger Kiska questions the lawfulness of the proposed ban and the ability of people to willingly seek out counselling.
He said that a law targeting 'talking conversion therapy' would have "significant legal and social consequences, particularly for those who have legal capacity and desire counselling, for their own reasons, to move away from same-sex attraction or behaviour, or to reconcile their gender identity with their biological sex".
The legal opinion warns that counsellors could fall foul of the law.
"A ban could also affect practitioners caught up in an overly broad or ill-defined ban on 'conversion therapy', despite practising within a peer regulated and ethical framework. This could give rise to claims under Protocol 1, Article 1 of the European Convention on Human Rights," it states.
The government has been criticised over its handling of the promised ban after a double U-turn in which it first said it was dropping legislation, only to announce hours later that it was going ahead with it but not for transgender people.
The confusion prompted evangelical church leaders to write to the Prime Minister seeking "urgent clarification" while also warning that a poorly drafted law would make it "illegal for us to teach people and help people of every age to live according to the Christian understanding of marriage".
Liberal church leaders have written their own letter to the Prime Minister asking him to go ahead with the ban, including for transgender people.
Andrea Williams, chief executive of Christian Concern, said: "The government is being strong-armed by manipulative campaigns rather than following its own research that further legislation is not needed. The fear of upsetting privileged lobbyists runs so deep the Prime Minister capitulated within hours.
"No one has produced any evidence of what LGBT activists call coercive 'conversion therapy'. What the activists describe would already be illegal.
"The government's proposals would only stop people seeking the change they want to see in their lives. That is a basic freedom which the government should not try to take away.
"Whatever is announced by the government in May, the problems remain: the definitions are inadequate, human rights will be breached and there is no evidence that a ban will help anyone.
"In such a scenario we will face no alternative but to pursue legal action against any proposed legislation in this area."
