When Richard Cass abandoned all hope of seeing his son alive again, he wrote a valedictory letter to the Australian volunteers who had spent more than 10 days searching for the 19-year-old backpacker.

Cass, a teacher, was preparing to return home to Watford, Hertfordshire. He used the letter to pay a poignant tribute to Jamie Neale, the boy he thought he had lost in the Blue Mountains, west of Sydney.

“Last night I was unable to sleep,” he wrote, “so I have tried to put together some words to convey something of what my family have lost if my son remains unfound.

“There is much concern in my country about the behaviour of young men, with . . . their perceived shortcomings blamed on family breakdown. James came from a ‘broken home’. I forgot to marry his mother and we ceased to live together when he was three years old. He was raised on a council estate in north London.

“But this was a teenager who was never in trouble with the police, who left school last summer with A-levels in maths, chemistry and history.”

His son had worked as a laboratory technician to raise the money for a trip before his degree studies began at Exeter University, Cass went on. He was a blood donor and a recipient of the Duke of Edinburgh award, “kind and courteous”.

However, Jamie was no “humourless paragon of virtue”, he said. The two of them had once visited the grave of Karl Marx in north London “just to get in touch with history”, and Jamie had planned to fly from Australia to Hanoi and Moscow to “call on Lenin and Ho Chi Minh”.

“I believe any teenager who can arrange his tour of the world around the brilliant conceit of tracking down the cadavers of communist dictators is uniquely unique and very, very special indeed.

“This is the boy that I suspect I have lost for ever. This is the diamond my country has lost in this tragedy.”

Janet McGarry, a youth hostel executive who helped in the search, said the letter had had a profound impact on her: “I wept when I read that.”

Cass had arrived in Australia on July 8, confident that his son would be found. But by last Monday police had begun winding up the search.

“With every passing day now there’s much less hope of finding your son,” Superintendent Tony McWhirter, the police officer in charge of the search, had told him.

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