At least one hundred organisations have pulled out of a landmark LGBT Government conference planned for this year following the “unacceptable” exclusion of transgender people from plans to ban conversion therapy.

More than 80 LGBT+ groups have withdrawn their support from the global, UK-hosted conference, saying they will only participate if the Prime Minister reverts to his promise for a trans-inclusive ban on conversion therapy.

Separately, the Terrence Higgins Trust issued a joint statement on behalf of 23 HIV organisations, saying they will also not be supporting or attending the Safe To Be Me conference, scheduled for June-July.

It comes as religious leaders including the former archbishop of Canterbury wrote to Boris Johnson urging him to include trans people in a ban on conversion therapy.

Dr Rowan Williams is among the signatories of a letter sent on Monday to Mr Johnson to say there is “no justification for the ban on so-called ‘conversion therapy’ excluding trans people”.

Convener to the writing group, Steve Chalke, Baptist minister and founder of Oasis Trust, told the PA news agency it was a “clear act of discrimination” to exclude trans people.

He said: “We need this ban to be extended to provide protection, an umbrella if you like of care, a canopy of care over this most vulnerable community.”

He added: “We have waited four years around this and we can’t wait any longer. A ban on conversion therapy must be now and it must be a ban for everyone, for all people, for LGB and T people.”

Antonio Guterres at Pembroke College
Former archbishop of Canterbury Rowan Williams (Joe Giddens/PA)

Last week, Mr Johnson managed to stage two U-turns in the space of a few hours.

It was initially announced that ministers were scrapping plans to ban the practice, sparking a furious backlash.

A Government spokesman confirmed on Thursday that they were looking instead at ways of preventing it through existing law and “other non-legislative measures”.

However, within hours of the announcement a senior Government source was quoted as saying legislation would be included in the Queen’s Speech in May.

The Prime Minister was said to have “changed his mind” after seeing the reaction to the move.

The ban now set to be brought forward by the Government will cover “only gay conversion therapy, not trans”, ITV’s Paul Brand reported.

Stonewall said the LGBT+ community’s trust in the Government is “shattered” and was withdrawing its support “with a heavy heart”.

It said it is “appalling” that the PM would “so casually walk away from four years of promises to the LGBTQ+ community”.

The charity said: “It is apparent that trans people have once again been sacrificed for political gain.

“Commissioning a separate body of work to unpick something that has already been resolved many times the world over, can only be read as an attempt to kick the issue of protecting trans people into the long grass.

“This is callous and unacceptable.”

The statement was shared by The LGBT+ Consortium, which has more than 500 members, and more than 80 groups have added their names to it.

Paul Roberts, chief executive of the Consortium, told PA he had received messages from six organisations wanting to add their names to the statement in the past 10 minutes.

He said: “We expect that number to grow massively over the next few days, as more and more member organisations see the message.”

A Government spokesman said: “The Government has a proud record on LGBT rights, and the Prime Minister is committed to bringing forward legislation to ban conversion therapy.

“Recognising the complexity of issues and need for further careful thought, we will carry out separate work to consider the issue of transgender conversion therapy further.

“This is a legally complex area and we have a responsibility to ensure unintended consequences are not written into legislation, particularly in the case of under 18s.”