Church of England bishops have been warned they must embark on an honest dialogue about gay clergy and laity if they are to avoid the church reaching "a tipping point where it is too morally discredited to be respected on any issue".

Before a meeting at which bishops are expected to finalise a review of the church's position on civil partnerships, the Christian gay rights network Changing Attitude has written to every member of the episcopate urging them to "speak the truth" about the role played by homosexual people in the church.

"The public stance of the Church of England towards civil partnerships in church, the disastrous submission to the government's equal marriage consultation, and the culture of the church, which forces so many to hide their sexuality – all these things are doing immense harm to the mission of the church in England," writes the Rev Colin Coward in a letter sent to bishops last week and published on Thursday.

In response to a government consultation on the legalisation of same-sex marriage, the church made clear its opposition to such a move earlier this year, prompting relief among conservative members but anger among liberal and gay Anglicans.

Coward, a gay man in a civil partnership, adds: "If the church does not want to reach a tipping point where it is too morally discredited to be respected on any issue, it is vital that its senior figures start, this year and next, to speak the truth."

The appeal comes as a group of bishops chaired by the Right Rev Robert Paterson, bishop of Sodor and Man, prepares to publish its findings on how the church's position on same-sex relationships should be reviewed in light of changes such as the growing number of clergy in civil partnerships.

As well as stating the church's belief that marriage is a union between a man and a woman, a pastoral statement issued in 2005 said clergy should not perform blessings for civil partnerships and were allowed to enter into same-sex civil partnerships providing they were celibate.

The church announced last year that the time had come for this statement to be reviewed, and the group of bishops is expected to meet in December to conclude the review. Their findings will be followed next year by a more wide-ranging report from a group chaired by Sir Joseph Pilling, a retired civil servant, on the Church of England's approach to human sexuality.

Coward urged the bishops to be honest with each other during this "critical period", calling on those meeting in December to publish recommendations which will begin "to transform the place of LGB&T [lesbian, gay, bisexual and transgender] people" in the church.

He appealed to them to acknowledge that the official position of the church on gay relationships was not reflected in the pastoral practice of many bishops who support and ordain gay clergy, including those in civil partnerships. He urged those with knowledge of same-sex relationships to come clean about their experiences.

"We need you to be honest about who you are, what you really believe about the place of LGB&T Anglicans in the church and what you actually do in your dioceses, remembering that your discussion will affect all of you," he writes in the letter.

A Church of England spokesman said: "There are gay men and women serving in various roles throughout the Church of England. Some will be volunteers, others in training for the priesthood, some as serving priests and others as bishops. We distinguish sexual orientation from sexual conduct where all Christians, whether straight or gay, are encouraged to live their lives in fidelity to biblical principles."

Among the issues being considered in the review of the 2005 statement is the hotly debated question of whether clergy in civil partnerships should be eligible for nomination to the episcopate. The dean of St Albans, Jeffrey John – a gay man in a celibate civil partnership – has been twice in line to become a bishop only to see his appointment founder amid outrage from conservatives. © Guardian News and Media 2012

[Anglican Bath Abbey in England via Shutterstock]