A social worker bought a homeless 17-year-old boy a tent to live in, a watchdog has found.
Cornwall Council even provided the "vulnerable" teenager with a replacement tent after the first one started leaking.
After approaching the council for help, the boy lived in the tent for five weeks, then a static caravan for four weeks and also spent several nights sleeping rough.
Following his ordeal during the summer of 2016, he was left emaciated and was detained in a psychiatric hospital for 11 months.
An investigation by the Local Government and Social Care Ombudsman found numerous failings in the boy's care by the council.
The inquiry suggested the council tried to place responsibility for the situation on the boy, rather than provide the right support to a vulnerable child who was suffering from drug addiction and mental ill-health.
The teenager, who has not been identified, had a history of cannabis use and suffered mental health problems.
After being arrested for drug dealing, he was not allowed to return to live with his father and the council housed him in supported accommodation in another town.
He was evicted from this placement for breaching conditions of his stay and became homeless.
The boy refused an offer from the council of supported accommodation 30 miles away from the area he knew.
A social worker then bought the boy a tent and helped him pitch it.
Council records show the boy's mother, who lived a long way from Cornwall, challenged the decision to place her son in a tent.
The council said no other options were available because the boy did not want to go into care.
The council asked the mother whether she could accommodate her son but she could not do so because of the risk to the other children she fostered.
Over the coming weeks the boy asked the council for accommodation on several occasions.
It also received two calls about his welfare, once after he had been found in an abandoned building having set fire to a mattress to keep warm.
At one point the council bought the boy a new tent after the first one started leaking.
After being moved to a static caravan, the teenager reported being sexually assaulted by a man in a car. There is no evidence that the council considered any action to protect the boy following this report.
Around a month later, the council moved the boy to bed and breakfast accommodation, which is against government guidance for housing teenagers.
Shortly after he was moved to appropriate supported accommodation and two weeks later he was detained under the Mental Health Act, which lasted for 11 months.
Michael King, the Local Government and Social Care Ombudsman, said: "There is a long list of failures in this case which had dreadful consequences for the boy.
"But the starkest, and most worrying, element is the attitude shown towards his situation.
"I would have expected an unequivocal response that it was simply wrong to accommodate the boy in this manner.
"It is true the boy in this case showed difficult behaviours. However, this is exactly why the Children Act exists - to support the most vulnerable in our society - and councils should not apportion blame when help is needed.
"I now hope Cornwall Council will take this investigation fully on board and use it to learn where it can improve things so it doesn't let other young people and their families down in such a way again."
The ombudsman ordered that the council should pay the teenager £2,500 and his mother £1,500.
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