16/11/2016 08:13 GMT | Updated 17/11/2017 05:12 GMT

My Film On Child Mental Health Was Deemed Too Dark. Tonight It Airs On Channel 4

Children who live with mental health and identity issues are often overlooked by the system and with the stringent cuts of recent years and increased numbers of referrals, they've never needed to be heard more than they do today.

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Ash is putting make-up on, which is not going to go down well with her mother. Ash's primary school doesn't allow make-up. They are strict about uniform too, grey trousers for boys, grey skirts for girls. But Ash has never had a problem with that; since the age of five she's worn a skirt to school. In almost every respect Ash is an ordinary nine year old girl. Except for one fact. She was born a boy.

I first approached the Tavistock and Portman NHS Foundation Trust about making a documentary series about Children and Young people's mental health more than five years ago. They cautiously agreed to meet me - but told me they were frequently approached and they always said no. There would be huge consent issues - how can a child make an informed decision to take part in something like this? How could we film therapeutic sessions without altering the therapeutic process? How would the child feel in years to come about their film?

But The Tavistock saw why it was also hugely important to try and give patients, or service users, a voice. Children who live with mental health and identity issues are often overlooked by the system and with the stringent cuts of recent years and increased numbers of referrals, they've never needed to be heard more than they do today.

When Josh's little brothers were babies sometimes he would have to look after them. Often there wasn't any food and he would try and look for it around the house. He remembers finding a tin of paint once and trying to eat some. But then he was only three years old. He's 12 now and he and his brothers have been adopted, but he still struggles with those memories.

The Tavistock bravely agreed to give us access but then we struggled to get the series commissioned. I was told it was "too dark" and "these issues have been well covered in TV documentaries already" but I was certain this privileged and unprecedented access to an iconic organisation would give us the opportunity to tell a bigger story about the state of our children's mental health and identity issues in 21st century Britain. A year went by, then Amy Flanagan, who had just finished making Bedlam at The Maudesley for Channel 4, was appointed as a commissioning editor at Channel 4 and she immediately saw the opportunity to make something that really mattered and commissioned the series.

Demi gets into fights on Facebook. She knows she shouldn't but sometimes she can't help herself. Her mum died when she was 11. She has Cystic Fibrosis and a history of self-harm, but she's also got a gorgeous laugh and wicked sense of humour. She'll be 18 next year so she'll be leaving child mental health services behind - whether she wants to or not.

First we had to figure out which services to focus on and to convince clinicians and service users to agree to take part. Understandably most were very cautious. It's a huge leap of faith to let documentary filmmakers into the most important and usually private aspects of your life. We met with all the different specialists and units that provide care for Children and Young People at the Trust, and we met 100s of young people and their families and carers. We met children from three to 18 years old. Gradually we built up relationships and slowly but surely, people started to trust us and one by one agreed to take part.

With the help of the senior teams at the Tavistock, and drawing on our previous experience of making films with vulnerable contributors, we drew up a series of protocols that we would work to. These firmly kept the interests of the young people in our series at the heart of everything we did.

In August, 2015, more than three years after I first approached the Tavistock we were ready to start filming. We now had our focus - the Gender Identity Development Service, Gloucester House - the Tavistock's day unit for children with emotional, social and mental health issues, and the CAMHS teams (Child and Adolescent Mental Health Service). Each film tells a very different story but offers the children and young people featured in them the chance to explain what life is like for them. They are very much at the centre of each episode. We feel it reflects the hard work of the Tavistock clinicians who support these young people but also highlights the challenges for the young people themselves. The series is a result of the collaboration of so many people. We are very grateful to them all. And five years on, it is even more timely.

Kids on the Edge is on Channel 4 on Wednesday 16 November at 10pm.