A 17-year-old boy who police feared would head to Syria to wage jihad has been kept alive following an "extraordinary level" of local authority intervention, a High Court judge has said.
Mr Justice Hayden said people often asked why time and public money was spent preventing teenagers from joining terror groups in the Middle East.
But he said in the boy's case a life had been saved.
The judge last year barred the teenager from travelling abroad - following a hearing in the Family Division of the High Court - after police and social workers raised concerns about him heading to Syria.
He made the teenager a ward of court - a move which bars him from leaving the jurisdiction of England and Wales.
And he has analysed the benefits of state intervention after reviewing the case at a follow-up hearing in London.
Mr Justice Hayden had been told that the boy's two elder brothers had been killed waging jihad in Syria
He said the teenager, who has joint Libyan and British nationality, could not be named.
But he said the local authority which had applied for the teenager to be made a ward of court was Brighton and Hove City Council.
"There has been an extraordinary level of intervention," said Mr Justice Hayden.
"It has kept him alive."
He added: "The thing that one hears most is 'why is so much time, money and effort spent in these cases? Why not just let them go? There is no doubt huge resources have been deployed in this case. And I myself have wondered whether that was proportionate. But at the end of the day ... they have saved a human life."
Mr Justice Hayden had made the teenager a ward of court in March 2015, when he was 16.
He had been told last year how council staff had learned that family members were making plans for the teenager to go on a trip to Dubai.
The judge had said he was concerned to ''keep this lad alive'' and said an order which barred him from travelling abroad was proportionate.
''(The teenager) is a vulnerable young person,'' Mr Justice Hayden had said.
''He has grown up in modern Britain in an extraordinary family - a family where the male members are patently committed to waging jihad in war-torn Syria.''
He said he had balanced the teenager's human rights and added: ''The balance falls clearly in protecting this young man, ultimately from himself.''
Barrister Martin Downs, who represents Brighton council, had told how the teenager's family had an ''extraordinary history''.
He had told how the teenager had an uncle who had been held in a United States detention camp in Guantanamo Bay, Cuba.
Three of his brothers had gone to fight for the al-Nusra Front - a group with links to al-Qaeda.
Two died when both were in their teens and a third was wounded.
A friend of the teenager had also been killed in fighting.
Mr Justice Hayden is expected to review the boy's case again in the near future.
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