The Church of England’s most senior openly gay cleric has said the source of leaked documents which cost him an appointment as Bishop of Southwark must be found before a replacement for the Archbishop of Canterbury is decided.

Dr John, 59, has twice had his appointment as an Anglican bishop blocked because of his celibate civil partnership. He has called the way the Church was seen as an enemy of gays “a disaster”.

The current Archbishop of Canterbury Rowan Williams announced in March that he would be stepping down after ten years as leader of the Church of England.

Dr John has urged steps to ensure the same person responsible for the leak which is believed to have cost him his appointment as bishop is not involved with the appointment of the new archbishop.

In a letter published in the Guardian this weekend, he wrote: “There is a matter which ought to be cleared up before the Crown Nominations Commission [CNC] meets to nominate the next archbishop of Canterbury.

“In July 2010 someone on the CNC leaked to the press the fact that I was a shortlisted candidate for the See of Southwark. The archbishop of Canterbury set up an inquiry into the leak under Baroness Fritchie. This inquiry was never published, and was said to have been unable to reach a conclusion.”

Dr John said the Very Rev Colin Slee, former dean of Southwark Cathedral, had been incorrectly suspected of leaking the document to “stir up threats of reaction among hardline evangelicals and frighten the CNC out of appointing me”.

Rev Slee was exonerated after his death in 2010 by a journalist who confirmed he was not the source of the leak.

Dr John concluded: “It would be good to know that steps are being taken to identify the real culprit and ensure that he will not be involved in nominating the new archbishop or in any further appointments.”

Last week it was revealed that Glynn Harrison, emeritus professor of psychiatry at Bristol University and one of the 16 members of the CNC panel said gay relationships “fall short of God’s purpose in creation”, and that there is “evidence that some people with unwanted same sex attractions can achieve significant change.”

In a statement issued by the Church of England, it was said he ”does not believe in the concept of ‘gay cure’ or ‘gay conversion’ and has never been involved in offering any formal counselling or ‘therapy’ in this area himself”.

He would support counselling for people who want to “manage and integrate their sexual desires with a religious identity grounded in the traditional teaching of their faith.”

The statement adds: ”Prof Harrison also notes however that there are anecdotes in the research literature, and in popular media, about individuals who have experienced some degree of change in either the strength or direction of their sexual attractions.”