It’s been a decade since I’ve made a film in the UK. I’ve been distracted by other human stories in countries as far-flung as Japan, Syria and Yemen, so returning “home” to Hull wasn’t easy. I joked that swapping my love of hummus in the Middle East for a journey to the middle of the lonely country (as Philip Larkin put it) and the mushy peas of Hull was going to be difficult.

But the question of working-class voices and poverty in Britain had been on my mind for a long time. My mates are a funny mix of well-educated, ordinary, working-class men and women who do a variety of jobs. Somehow they never find themselves represented in TV and film – in fact, of late, they have found themselves horrendously misrepresented, especially in nasty, hate-filled poverty porn shows. I remember growing up with classic TV series such as Boys From the Blackstuff that presented a dignified working class under attack. Today’s shows are about shirkers, skivers and soap dodgers.

So I wanted to understand where we’re truly at as a country. With my city, Hull, suffering from high unemployment, child poverty, and placed in the spotlight as the UK city of culture in 2017, I wondered what culture meant to the residents.

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A Northern Soul, my new film, explores these questions. It follows Steve Arnott over the course of a year, as he sets up his hip-hop project for disadvantaged kids – the “Beats Bus” – while trying to make ends meet in his low-paid, “in-work poverty” factory job. On the one hand, it’s a shocking portrait of poverty’s grip on Britain; on the other, it’s a celebration of a relatable, dignified, working-class grafter – standing for all those whose stories and voices aren’t being heard. And the stories all involve young people.

I was careful to secure funding partners – the Joseph Rowntree Foundation, BBC2 and the British Film Institute – that would help to get this crucial narrative seen. When, ahead of the film’s national cinema release, the film was sent to be certified by the British Board of Film Classification (BBFC), it never entered my mind that it wouldn’t be classified as a 12A (which means that it can be viewed by children under 12 in the presence of their parents, and over 12 without). At the opening night of the film at the Sheffield Doc/Fest, it was rated 12A by the Sheffield city council. It had also been given a 12A certificate by Hull city council for a series of preview screenings.

So I was amazed to see that the BBFC awarded the film a 15 – for strong language. This means that the very people affected by many of the issues portrayed in the film will not be able to see it. It is difficult to not see bias in these differing assessments.

The BBFC rating means that the film is considered inappropriate for children under the age of 15. Yet children of all ages have been attending the screenings with their parents for the last few weeks in Hull. When we asked these kids to tell us how they’d sum up the film, the two words that kept coming back were “empowering” and “inspirational”.

My film-making style is intimate and engaged – I look for “characters” whom I film over a long period of time and who let me into their lives fully. Finding people who can articulate their situation is important, and Steve’s dream of helping poor kids in Hull during the city of culture period seemed the perfect opportunity. Steve trusted me and talked openly and honestly. Trust and intimacy are things a documentary film-maker works hard for – they’re not easily won, and it is also a responsibility.

As a result, Steve speaks to me as he would to a mate – his language is real and engaging. He uses the occasional F-word, as most of us do in everyday language, but only ever in my company, never in front of anyone else, and this is never aggressive or sexual.

There is a limited amount of bad language in the film. There are 19 F-words: 14 from Steve, and five that feature in the song Sometimes by Akala, who appears briefly in the film on stage, singing the lyrics “When I feel like / Fuck it, I’ve had enough”. It’s the BBFC’s job to count them and apparently you’re not allowed more than four!

But the point isn’t the strong language – it’s about a voice and the everyday lived reality of someone being censored. It seems absurd that this would be deemed inappropriate for children, while films currently playing at the cinema receive 12A certificates despite gratuitous on-screen violence. Mission Impossible, 12A, has a scene of someone being shot point blank on camera, for example.

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There have also been exceptions to the rule – The King’s Speech was recertified as 12A because the swearing occurred in a speech therapy session. Is it different to see the King of England say “fuck”? Is it more threatening to hear poor northern people swear? Does an audience want to know how poor people actually live and speak? And if The King’s Speech was recertified due to “context”, that surely also applies here.

A Northern Soul is not a fictional feature film – it’s an ethnographic documentary that provides an accurate account of people’s daily lives in a humane and dignified way, which includes speaking both intimately and authentically. The classification means that kids under 15 – who were part of our key audience, and who would have benefited from it – will not be able to see the film. Instead, they will probably stay home watching movies of people blowing each other’s heads off or reruns of Love Island with continuous swearing and real-time fornication.

The BBFC has suggested that I make cuts to turn the film into a 12A. But that would feel more like censorship than classification, and I will not do this to Steve’s words. Whether or not this sets a precedent, I hope that the BBFC will reconsider their rating – just as they did with The King’s Speech.

• Sean McAllister is a British documentary film-maker