Proposals in a Private Member's Bill to ban so-called 'conversion therapy' would "very likely" be a breach of human rights law, a top lawyer has said. 

Labour MP Lloyd Russell-Moyle's Conversion Practices (Prohibition) Bill is being debated on friday. It proposes a ban on offering or advertising conversion practices, while also promising protections for parents and the practice of religion. 

Senior human rights lawyer Jason Coppel KC is not persuaded and has warned that the terms of the Bill are so "broad in scope" that they would criminalise expressions of personal conviction "even if they are made without expressions of hatred or intolerance".

He also said it would lead to a "serious intrusion" into the ordinary practices of churches. 

"Whilst some attempt has been made to craft exemptions or exceptions so as to ensure that the practice of religion is not prohibited, the central prohibition in the Bill ... remains a wide one, applying to churches and other religious organisations, and to those expressing certain views, including gender critical views, outside those settings," he said. 

Mr Coppel said that the Bill would interfere with religious freedoms protected by human rights law. 

"I consider that the Bill ... if passed, would constitute a serious intrusion into the legitimate activities and practices of Christian churches and religious communities, which would be contrary to their rights protected by the ECHR, and so to the Human Rights Act 1998," he said. 

"They would also interfere with the legitimate expression of gender critical views, again in a manner which would be likely to breach ECHR rights." 

That was his conclusion in a legal opinion provided to The Christian Institute, which is campaigning against the introduction of a conversion therapy ban. 

Simon Calvert, Deputy Director at The Christian Institute, said that the wording of the Bill was "sloppy" and definitions were "far too broad".

"If passed this would result in criminalising Christians and gender-critical parents for conversations which most people would consider perfectly reasonable," he said.

"This is not about protecting people from abuse. That is already illegal. There is no 'harm' test in the Bill. It is about punishing people for talking.

"Each iteration of a conversion therapy ban we have seen, whether at Westminster or Holyrood, has raised the same issues.

"It is impossible to legislate in this controversial area without trampling on basic human rights."