Among others, the letter was co-signed by Rev Colin Coward, founder of Changing Attitude England, the Very Rev Michael Sadgrove, Dean Emeritus of Durham, and Canon Jeremy Pemberton.

"We need to know whether you are able to express public support for the full equality of LGBTIQ+ people in ministry and relationship in the Church of England," they wrote.

"This includes permitting those going forward to selection for ministry and for licensed Readers and clergy to marry same-sex partners and to conduct same-sex marriages in church and bless marriages and civil partnerships with the same parameters applying to opposite sex marriages.

"Unless this is clarified before any next steps process begins we will be unable to be involved with it or support it. We need you to provide this clarity as a matter of urgency."

The letter was issued in direct response to a film released by the Church of England Evangelical Council (CEEC) - a group founded by the late John Stott. 'The Beautiful Story' is pitched as a "30 minute film that explains how a biblical vision for human sexuality is good for individuals, the church and society as a whole".

While critics have said that it is damning of LGBT people, the makers insist that the film is "intended to galvanise and support discussion in local churches around sexuality and relationships" and "provide the case for what many call a traditional Christian viewpoint".

In his introduction to the letter, Rev Coward argues that the film makes it "impossible" for the group to "participate safely" in the upcoming discussions. "The videos show that LGBTIQ+ people will risk encountering abuse and homophobia at any meeting or event held as part of the LLF process," he wrote.

Following the release of the LLF resources by the Church of England addressing issues of sexuality, the Bishop of Blackburn, Rt Revd Julian Henderson, who is also the President of CEEC, said that he "will look closely at the materials", noting that they must be evaluated "in the light of Scripture".

"While discussions about these issues are always welcome, the key question is not one of church procedure but whether we think that the teaching of Scripture is right," he added. "So we will engage, but this is actually about obedience to Scripture."

At one point in the CEEC's film, Henderson floated the idea of leaving the Church of England entirely over the issue.

"I'm not sure there are many of us in the Church of England who want to leave," he said. "But as and when the church gets to the point where it changes its teaching and liturgy and its practice in these areas...is going to be a moment for people to have to reconsider their allegiance to the church."

He added: "At the moment, I want to be in the Church of England, I want to fight for the traditional teaching of the church on these matters.

"But the time may come when it's going to be essential for those who hold to scriptural teaching on marriage and same-sex relationships to say 'we cannot operate under this particular system and support this kind of doctrine and practice within the life of our church.'

"And then may lead to having to look for alternative solutions."

Archbishop Justin Welby bills the Living in Love and Faith project as a "way of enabling us to think together about identity, marriage and sexuality".