The Archbishop of Canterbury apologised unreservedly on Wednesday after it emerged he worked at a Christian youth camp whose leader is alleged to have physically abused young boys.

Most Rev Justin Welby says the Church "failed terribly" by not reporting John Smyth QC, who ran the Iwerne Trust's summer camps, to the police. Allegations to be broadcast on Thursday night on Channel 4 News claim Smyth used the camps to access young boys and carry out "horrific" sado-masochistic attacks in the 1970s.

There is no suggestion any abuse took place at the UK camps themselves, however.

Smyth forced boys to strip naked and subjected them to savage beatings to "help you become holy", according to one victim Mark Stibbe. They were a punishment to purge them of such sins as masterbation and pride, victims said.

Although the Church of England was made aware of the abuse in 1982, it failed to report it to the police, the Channel 4 investigation found.

Welby worked as a dormitory officer and a mentor at the Iwerne retreats, which were known as "Bash" camps and aimed at public school teenagers.

A statement from the Archbishop said: "We recognise that many institutions fail catastrophically, but the Church is meant to hold itself to a far, far higher standard and we have failed terribly.

"For that the Archbishop apologises unequivocally and unreservedly to all survivors."

He added on LBC radio on Thursday morning he was "completely unaware" of any beatings going on while he was working at the camps.

"I never heard anything at all about any abuse," he said. "I had no suspicions."

The assaults were carried out over a three-year period in the late 1970s and only came to light in 1982 when one victim, then a 21-year-old student at Cambridge, attempted to commit suicide after being told he would be beaten again.

An investigation was launched at the time by the Iwerne Trust and carried out by a vicar and friend of the Archbishop, Mark Ruston. But despite concluding that "the scale and severity of the practice was horrific", Smyth was not reported to the police.

Welby says he was not aware of the allegations and says he kept occasional contact with Smyth.

The Archbishop was only made aware of the allegations in 2013 when it was eventually reported to the police.

A Lambeth Palace statement on Wednesday said: "John Smyth was one of the main leaders at the camp and although the Archbishop worked with him, he was not part of the inner circle of friends; no one discussed allegations of abuse by John Smyth with him."

The Church of England has echoed the Archbishop's "unreserved and unequivocal apology to all the survivors" and said its team of six full time safeguarding officers would review all the files to see what more could have been done.