Fonagy said the support being provided to young people needed to be improved.
The NHS, he said, was simply “not fit for purpose”.
He said too many people were being left on waiting lists, pointing to figures that show one in three people referred to mental health services were still waiting for help after a year.
There were some positives steps being taken, he said, including the rollout of mental health teams to work closely with schools.
However, he said tackling the problem will require action across society – in education, employment, housing and families themselves.
For example, Fonagy blamed cuts in youth services over the past decade or so for leading to fewer places for young people to mix and develop a sense of belonging.
“We need to have opportunities for them to participate, because participating in things… maintains good mental health.”
He also said it was striking that loneliness among young people had increased since 2000, linking it to the rise in use of phones and social media, which have reduced face-to-face contact and disrupted sleep patterns, both of which are damaging to mental health.
But as well as addressing phone use, he said there were other things families and friends could do.
“Saying to someone, ‘I notice you’re not quite the same as yesterday. Is there anything the matter?’ Knowing there is someone who knows makes an enormous difference.”
His hope? That working together, society can make a difference. “I want young people to hear that when they feel anxious, depressed or distressed, that it’s a real problem, but a problem we can do something about.
“When I needed help, I got it. I want everyone to have that chance.”
