A council has said sorry over failings in its dealings with Parsons Green bomber Ahmed Hassan.
The 18-year-old, who lived in Sunbury, Surrey, told immigration officials he had trained with Islamic State after he arrived in Britain illegally in 2015 and claimed asylum as a child.
Hassan was referred by Barnardo's and Surrey social services to Prevent, but kept his plans to cause carnage a secret.
He was said by police to have engaged with the de-radicalistion scheme Prevent through its Channel programme while keeping his plot secret.
Deputy Assistant Commissioner Dean Haydon, of Scotland Yard, said: "On the one hand he was appearing to engage with the programme, but he kept secret what he was planning and plotting."
The high-achieving college student kept his "dark thoughts" from his foster parents, college mentor and other agencies who all tried to help him have a better life.
In his sentencing, Mr Justice Haddon-Cave said he was sure Hassan had in fact been trained with IS before he committed his act of terrorism.
Afterwards, a Surrey County Council spokesman said: "Our work with other agencies in this case wasn't as good as it should have been and we're sorry for our part in that.
"We knew before the terrible incident at Parsons Green that we needed to make changes and had already begun to do so.
"Since then we have made further improvements and continue to focus on ensuring our work in this area is as good as it can be. Our thoughts remain with everyone affected."
The spokesman said staff from agencies on the Channel panel had met Hassan many times between February 2016 and September 2017.
He received "extensive support" in mental health and education and the panel monitored and reviewed it.
The spokesman added: "This was a difficult case in tough circumstances. We have a duty as a county council to provide support to unaccompanied asylum-seeking children who arrive in Surrey and we're also expected to work with law enforcement agencies and others to help stop people being drawn into terrorism."
A review of Hassan's dealings with Prevent is under way.
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