Ms Blay said children are asked to kill themselves in front of a webcam

Historian Celia Blay, from Maidenhead, said she came across the man when speaking to a troubled teenager.

He makes contact with vulnerable children and encourages them to take their lives while he watches them through a webcam, she said.

Ms Blay claims she has discovered he is based in the US Midwest and has reported it to the police.

She said she stumbled across him while she was having an online conversation with a troubled teenager she was trying to help.

[He] is very sympathetic but never, ever suggests that they seek help

Celia Blay, historian

"He doesn't really mind who his victims are. He tells them how to hang themselves and how to hang themselves in front of a webcam," she said.

"He is very sweet, he pretends to be an emergency room nurse.

"He calls them 'hun' and 'darling' and this sort of thing and is very sympathetic but never, ever suggests that they seek help."

Paul Kelly, from the suicide prevention charity Papyrus, said the current law cannot do anything to stop such people.

In 2001, Mr Kelly's son Simon took his own life after obtaining instructions from a an internet suicide website.

Mr Kelly said: "The Suicide Act goes back to 1961, which obviously predates the very existence of the internet and we regard it as being quite ineffective to challenge the current development."

He added that there was very little police could do in such cases, unless there were clear links and proof connecting the predator with the victim.