An abuse victim who suffered years of savage beatings at the hands of John Smyth, a Christian youth camp leader, has written an open letter to the Archbishop of Canterbury outlining the scale at which the activities were ignored and covered up by several organisations including the Church.

The letter published in the Telegraph, simply signed "W", details how the victim tried to commit suicide when faced with a "special beating" for his 21^st birthday.

It demands Justin Welby question himself – think "very carefully about this," the victim says. "Whose side have I been on, all this time? The side of the victims. Or the side of the abuser?"

It comes after the Bishop of Guildford, Andrew Watson, revealed he was also a survivor of a "violent, excruciating and shocking" beating by Smyth, who was a UK barrister and QC.

Smyth ran Christian summer "Bash" camps under the auspices of the Iwerne Trust and is alleged to have beaten as many as 22 boys who attended the camps over a series of years. The attacks only stopped when one victim, the author of the anonymous letter, attempted to commit suicide.

An investigation was then launched by the Iwerne Trust but, despite the possibilty of criminal activity being raised, nothing was reported to the police.

Justin Welby was a young leader on the camps and knows Smyth but says he had no knowledge of the abuse, which is not alleged to have taken place at the camps but in a shed at the bottom of Smyth's gardens.

The survivor describes in the letter how he "latched on to" Smyth who was "probably the first man who seemed genuinely interested in me".

But over a period of four years he received "thousands and thousands of lashes" every four to six weeks.

"My body couldn't take it any more," he writes of his attempted suicide in 1982. "My mind was frozen in trauma. I was ready to die. Death would have been a relief."

He describes being "overjoyed" and "elated" when along with a group of victims he discovered Channel 4 was investigating the abuse.

"We knew everything that he had done to each of us. How appalling it had been. How cruelly and malevolently he had used some individuals in particular. That went without saying."

He said before that investigation, no one had contacted them from the four institutions involved, despite the abuse being reported.

The letter is particularly critical of the The Titus Trust, which took over the running of the IwerneTrust. Despite being advised to report Smyth's abuse to the police and conduct an investigation, they did not conduct an inquiry and removed the adviser from his role, according to the Telegraph's letter.

But Welby also comes in for criticism as "an observer" – someone "who knew but never reported appropriately".

He says Welby should ask himself: "I knew about John Smyth. I become aware about some of the things that this abuser did, I have 'observed' them. Can I look myself in the mirror and honestly say that I did everything I could to report to the correct authority all the things that I knew? Did I give the people who might bring the abuser to justice every scrap of information that they might need?"

Welby has repeatedly denied knowing anything about any abuse while he worked at the Bash camps. In a statement last week he said he left the camps to work in Paris from 1978 for the next five years, when the abuse is said to have happened.