"I always used to nag him about wearing a fluorescent vest when he was on his bike. I think he was saying: "Don't worry, Mum, I'll be all right."

His father Jeremy said his son was not usually affectionate but the night before he disappear he rested his head on his shoulders.

"Arthur wasn't very physically affectionate," he said.

"He was as a child, not as a teenager. He did used to do this thing, though, where he'd come up behind me and lean on my shoulders. He did do it the night before he left. I thought, "that's nice" because he hadn't done it for a while."

The couple say they are "haunted" at the thought he might be dead.

When he failed to return home from school that night, his mother drove around searching for him and even ran down an shortcut in the dark looking for a body in the ditches.

His father said they are consumed by an "alarm of panic".

It was the next day a letter arrived from him in the post, in which Arthur told them: "I know you will be upset, but understand that I have to do this."