A decision by a major Christian organisation last week marks a major setback in the ongoing struggle for LGBT inclusion in churches in Britain. A body that exists to promote unity between Christians of strongly different views has prevented their duly appointed co-president from taking up her post – because she is married to a woman.

Churches Together in England (CTE) brings together churches that used to persecute each other, to sit down together and strive for common ground. Catholics whose predecessors burnt Protestants at the stake emphasise their unity with them as fellow Christians. Evangelicals who in the past broke into bitter rivalries with each other over their view of infant baptism now regard the issue as of relatively minor importance. CTE, which is far from being an especially conservative organisation, is by its nature a grouping that invites Christians to seek for unity amidst difference and to promote dialogue even when it is uncomfortable and challenging.

Yet last week CTE undermined its own mission and abandoned any reasonable claim to be a serious voice for Christian unity and dialogue. They blocked their duly appointed co-president from taking up her position, because she is in a same-sex marriage.

CTE structures are complicated. It is not necessary to understand every detail of them to grasp what is going on here. There are six presidents of CTE at any one time. Some hold the role because of their position in their own denomination, such as the Archbishop of Canterbury and the Roman Catholic Archbishop of Westminster. Others are appointed by groups of churches. The Fourth President, for example, represents a number of Christian denominations, including the Religious Society of Friends, better known as Quakers. This year, it was the turn of the Quakers to nominate the Fourth President. After an internal process of prayerful discernment, the Quakers nominated Hannah Brock Womack, a prominent peace campaigner and former employee of War Resisters’ International.

After months of faffing about, CTE announced on Friday that they had blocked Hannah from taking up her position because she is married to a woman. The Fourth President will be replaced at meetings by an “empty chair”.

My reaction to this news is affected by the fact that I have been honoured to call Hannah a friend for several years, and to have campaigned alongside her many times. I have a lot of admiration and respect for her. But I would be almost as angry and upset about this decision even if I had never met, and knew nothing about, the person concerned.

The nature of CTE is that people who strongly disagree, who may not even trust each other, who feel uncomfortable around each other, are invited to sit down together and engage in dialogue. I am more than happy to engage in dialogue with people who oppose same-sex marriage. I know that many (though far from all) such people are open to genuine dialogue with LGBT Christians and other supporters of same-sex marriage.

But CTE’s decision is a kick in the teeth for attempts to promote dialogue on this issue. The decision implies that same-sex marriage is a more important issue than all the other issues that CTE presidents, and members, disagree about. Some of these are issues that their predecessors literally killed each other over.

CTE presidents may be Protestant, Catholic or Orthodox. They may be liberal or conservative. They may believe in transubstantiation, consubstantiation, the Literal Presence, the Virtual Presence, papal infallibility, biblical infallibility, biblical fallibility, evolution, creationism, capitalism, socialism, pacifism, just war, holy war, substitutionary atonement, Christus Victor atonement, salvation by grace, salvation by works, infant baptism, believers’ baptism, baptism in the spirit, the authority of priests, the priesthood of all believers, purgatory, no purgatory, literal hell, metaphorical hell, annihilationism, universalism, premillenialism, postmillenialism or amillenialism. All these things are acceptable for CTE presidents. The one thing that is not acceptable is marrying the person you love, if they happen to be the same gender as you.

There are a few beliefs that are not acceptable within CTE, such as rejection of the Trinity or disbelief in the divinity of Christ. Excluding a president because she is in a same-sex marriage puts attitudes to marriage and sexuality on a level with these basic Christian doctrines. This is not only homophobic. It is theologically ludicrous.

Anti-LGBT attitudes within Christian churches are not confined to small numbers or even to the most conservative churches. They are present within mainstream, even liberal, church structures, defended by those who don’t want to rock the boat or who want to sweep controversy under the carpet. The news from CTE is a reminder that we cannot defeat homophobia within Christianity by quietly waiting for change or by playing down the importance of the issues. LGBT Christians and their allies, and all who believe in genuine dialogue, must speak out.

CTE’s vile decision is accompanied by the usual hateful words that are supposed to soften the blow while only making it harder. Their statement declared that they recognise the “hurt” that has been caused to Hannah, and to Quakers. I’ve got used to church leaders saying they recognise the hurt that has been caused to LGBT Christians, even while they continue to hurt us. This is rather like being repeatedly punched in the face by someone who tells you that he knows his punches are hurting – while he’s still punching you.

Churches Together in England have said that for the duration of Hannah Brock Womack’s term of office, she will be replaced in meetings by an empty chair. They have unintentionally created a very accurate image of the role that LGBT Christians are allowed to have in Christian churches: a chair, with nobody sitting in the bloody thing.