A former mentor for the Parsons Green bomber has said the teenager had not agreed to take part in the government's deradicalisation programme Prevent.
Kayte Cable, Ahmed Hassan's mentor the year before the September 2017 attack, said his lack of consent meant he was not properly engaged with the scheme.
Hassan, 18, injured 51 London commuters last year with his homemade explosive.
Police maintain that the Iraqi asylum seeker was co-operating with the programme at the time of the attack.
Surrey County Council, which was responsible for Hassan's care, said it "didn't need" his consent to enrol him in the Prevent scheme in 2016, as he was then underage.
The Metropolitan Police said Hassan appeared to be engaging with its Channel programme, part of the Prevent deradicalisation scheme, when he planted the bomb at the London Underground station a year later.
Channel operates on the basis that people regarded "at risk" agree to take part.
A council spokesman said: "Because Hassan was under the age of 18, or claimed to be, we didn't need his consent to put him onto Channel.
"The county council gave consent on Hassan's behalf because he was under our care."
Hassan's former volunteer mentor, college lecturer Ms Cable, told the BBC that lack of consent meant the teenager was not properly engaged with the programme intended to deradicalise him.
She said: "It is a matter of conscience for me that we learn from this terrible event and do everything in our power to ensure that nothing like Parsons Green ever happens again.
"If we don't have complete transparency about what happened, I don't see how this is possible."
He had been alerted to police and Prevent for comments made in a January 2016 immigration interview, when Hassan claimed he had been recruited by the Islamic State group in Iraq and had been "trained to kill".
Hassan, who arrived in the UK as a child asylum seeker, has been jailed for a minimum of 34 years after being found guilty of attempted murder.