It was January, 2008, just before his 21^st birthday and he'd made a plan to run away from the London psychiatric hospital he'd been admitted to the previous month.

Jonny had just been diagnosed with schizoaffective disorder, a combination of schizophrenia and bipolar, and felt overwhelmingly "bleak" about his future.

"I gave up," he says.

"I thought there is no way I can come back from this, no way I will ever recover."

So he escaped and ran to Waterloo Bridge, climbed the railings and sat on the ledge ready to jump.

The details are hazy now but what he will never forget is that a stranger stopped, quietly stood next to him and began talking.

"This guy just came out of nowhere, I didn't want to talk to him but he said 'I'm not going anywhere'; he was kind, gentle ... there was something about him and I warmed to him," Jonny recalls.

The stranger talked and gradually Jonny opened up to him.

"In hospital there had been no one to talk to, which seems a strange thing to say," he says.

"I was on suicide watch so people would watch me - they would watch me go to the toilet, to the shower - but they never spoke to me.

"It was dehumanising.

"And here was this guy who just wanted me to talk and was OK with the fact I was suicidal.

"He just cared - and he literally changed my mind."

Eventually the stranger convinced Jonny to join him for a coffee but as they left the bridge, police were waiting, he was taken away, sectioned and returned to hospital; the kind passerby a fleeting memory.

But somehow, something had shifted in Jonny.

"I felt different because of his kindness, I felt some hope that perhaps I could overcome," he says.

"Someone had believed in me."

Jonny's struggle with mental health and his sense of self started at a young age.

His parents took him to a psychiatrist when he was five - "I stopped sleeping, I was anxious and violent" - and he struggled to fit in at school despite being academically gifted.

Navigating his teens was even more traumatic; he heard voices, became depressed and started questioning his sexuality.

"I come from a Jewish background where you are told being gay is a sin and this had a massive impact on me," he reflects.

"At 17 I went to my doctor because I was struggling with suicidal thoughts.

"He was great and gave me a referral to an adolescent mental health service but they had a long waiting list so I gave up."

In his third year of university, Jonny became so unwell he was sent home to his parents.

"I became psychotic - I lost control and felt like I was being possessed," he says.

"It was very frightening for me."

It was at that point Jonny was admitted to the psychiatric hospital where he was diagnosed.

Being returned to that same hospital after his escape and plan to end his life was particularly hard, he admits.

But Jonny held on to the glimmer of hope gifted to him by a stranger.

It was to be the start of a long journey, of years of trying to find the right psychiatrist, the right treatment plan and, most importantly, self-acceptance.

"I always say to people now don't give up - there will be someone out there (to help)," he says.

"It's so important with therapy to have that space where you can be open and honest."

It's been a "massive journey" for Jonny's parents as well; at the time there was simply no education or information available to them.

"Dad now runs a father's forum working with men whose children are struggling and he gives talks with me," Jonny says proudly.

"My psychiatrist involves my dad, he explains things really well and this has strengthened our relationship.

"And now I don't hide from my friends if I'm struggling and that makes a huge difference."

Jonny has discovered a deep well of peace through mindfulness and Compassion Focused Therapy (CFT).

"Everyone recommends meditation and to be honest it took me a while to get into it," he admits.

"It's like going to the gym; it takes a while to change the way the muscles work in your brain."

He's learnt to practise kindness - to himself.

"I don't beat myself up, I accept that this is a sh*t day or a sh*t week ... it's about being more compassionate to myself."

Jonny also learned to talk - to speak his truth to family, to friends and to the wider world - about his struggles, even those suicidal thoughts.

In 2011 he started making films on YouTube about his condition (that have been watched by millions) and became involved in mental health charities.

"I wanted to talk and help others and I had lost so much confidence after my diagnosis, I struggled to find a purpose," he reveals.

The more he spoke and the more videos he made, the less shame he felt.

Six years to the day after that fateful encounter at Waterloo Bridge, Jonny launched a social media campaign through Rethink Mental Illness to #FindMike, the stranger who turned his life around.

Launched on January 14, 2014, the video was shared to Facebook and Twitter and within 24 hours had been viewed more than a million times (eventually reaching 300 million people worldwide).

The campaign went viral and within two weeks the real 'Mike' (Neil Laybourn) had been found.

They met at a pub in London, both men nervous about what to expect.

"It was a really big deal," Jonny says frankly.

"It was overwhelming but in a good way. We gave each other a hug and it felt like we were old friends.

"The memories started falling into place, of the bridge, of him.

"I thanked him and Neil was so humble; he didn't want to accept my thanks. He said, 'You've done the work to get yourself to where you are'."

Their emotional reunion became the basis for the acclaimed documentary, The Stranger on the Bridge, and a friendship that has seen the pair become powerful ambassadors for suicide prevention.

In 2017, Jonny received an MBE for his services from Prince William, the Duke of Cambridge, who also wrote the foreword to his first book.

The prince has publicly praised Jonny for his "bravery, passion and determination".

"Mental health is not a dirty word - we all have mental health like we do physical health, good or ill," he wrote.

"But I have seen time and again how not seeking help when it all seems too much can impact the rest of our lives."

Jonny is a passionate champion for people living with mental illness but he worries particularly about the lack of services for young people and their declining mental health - in the UK and across the world.

He worries about the over-use and unrealistic expectations of social media, cyber-bullying and the determined focus on academic merit over mental wellbeing in education.

This week he launched a new youth mental health charity, Beyond, which aims to provide grants to groups that work with youth, their families and educators.

"Mental health services for young people are not in great shape," he says.

"The children's commissioner (UK) says 75 per cent of young people with mental health issues are not receiving treatment and yet suicide is the biggest killer of young people in this country."

His own experience is a brutal reminder that three-quarters of all mental health issues begin in adolescence and yet many young people do not get the help they require.

"There is still a long way to go," Jonny muses.

And so he continues to talk, to speak out and to remind others there is a way out of the "absolute hell, the absolute darkness, the absolute despair" that once consumed him.

Just as that stranger on the bridge did for him all those years ago.

"I spent so many years waking up wishing I was dead to waking up now grateful to be alive," he says.