Barney Platts-Mills, who has died aged 76 after a period of ill-health, wrote and directed one of the freshest films of postwar British cinema. Bronco Bullfrog (1969) was made in black and white for just £18,000; shot on location in Stratford, east London, it starred teenagers with no professional acting experience.

Platts-Mills met many of them while making a short documentary, Everybody’s an Actor, Shakespeare Said (1968), about the theatrical pioneer Joan Littlewood and her improvisatory workshops at the Playbarn. “The local young teenagers who would otherwise vandalise her theatre and torment her actors on the way home were here given a place of their own,” he said.

Bronco Bullfrog featured Del Walker, an apprentice plumber for Newham borough council at the time, as a welder also named Del. His faltering romance with the 15-year-old Irene (Anne Gooding) faces assorted problems and pressures, including their mutual boredom and poverty, his criminal inclinations, and, most damagingly, the prejudices of her mother (she thinks Del is an oik) and his father (who considers Irene snooty). Denied a place to be intimate together, they end up with a local petty criminal (the title character, chirpily played by Sam Shepherd), who gives them a bed among his stolen goods.

Platts-Mills balances hope and despair, joy and bareknuckle toughness. The grimy, desolate locations show these youngsters to be products of their environment, but a resilient good humour endures in them, and in the film. In one scene, Del buys a cinema ticket, then opens the fire exit in the auditorium to admit a handful of his pals, only to find a whole queue of expectant freeloaders headed by a cheery pensioner.

The visual style could be scrappy, the acting unpolished, but that was part of the charm. “Barney just said, ‘Do it the way you’d do it really,’” recalled Gooding. There was a script, the director confirmed, but “sometimes the cast used it and sometimes they did not”.

Praise for the picture was near unanimous. Alexander Walker in the Evening Standard said: “It sends your heart leaping.” The director Lindsay Anderson called it “a very, very good film indeed, not just promising but a promise fulfilled”. Jay Cocks, the Time magazine critic and future screenwriter, noted that “there is hardly a moment that does not display a vigorous, very real talent”. Many predicted a bright future for the film-maker.

That wasn’t quite what happened. Bronco Bullfrog may have survived almost being killed at birth – it had been “rejected by several who should have known better”, noted Derek Malcolm in this paper, alluding to the director Bryan Forbes, who had expressed an interest in financing the script until he saw Platts-Mills’s short about Littlewood’s workshops. “I could do better with my children on the lawn,” he said.

The finished film, however, was hamstrung by slapdash distribution. It was pulled from one central London cinema after only 18 days to make way for a royal premiere, prompting a rowdy protest by the cast and their friends. (Princess Anne later responded to a letter of apology sent by Shepherd, and attended a special screening of Bronco Bullfrog at the ABC cinema in Mile End.) It played at Cannes in 1970 but was largely forgotten thereafter. The master negative was even dumped in a skip, and rescued only by a quick-thinking grader. Rereleases in 2003 and 2010 saw its reputation restored.

Barney was born in Colchester, Essex, to John Platts-Mills, a barrister who was briefly a Labour MP until his expulsion from the party in 1948 over his socialist sympathies, and Janet (nee Cree), an artist. He was educated at Bryanston school, Dorset, and left at 15 with hopes of becoming an actor. His father asked for advice from the director Lewis Gilbert, who told the boy: “You don’t want to be an actor. You want to tell them what to do.”

Gilbert employed him as third assistant trainee editor on The Greengage Summer (1961). Platts-Mills also assisted the sound editor Winston Ryder, who was busy on the soundtrack to Spartacus (1960). Later he showed the main characters of his second film, Private Road (1971), going to see Stanley Kubrick’s epic on their first date.

After a spell in the cutting rooms at Granada Television, he worked with John and Marlene Fletcher, who had been associated with the Free Cinema movement. Inspired by them, he formed with the director James Scott and the cinematographer Adam Barker-Mill his own company, Maya Film Productions, with financial help from Nicholas Gormanston, the premier viscount of Ireland; they were soon joined by the producer Andrew St John. Early Maya works include St Christopher (1967), Platts-Mills’s documentary about Rudolf Steiner schools for children with disabilities.

Private Road was another acutely observed study of a relationship under unreasonable strain. Made in colour on a slightly larger budget (£26,000), it featured professional actors, including Susan Penhaligon and Bruce Robinson (later the writer and director of the 1987 comedy Withnail and I) as well-to-do sweethearts. They were plagued nevertheless by many of the same problems of the Bronco Bullfrog gang: how to realise one’s dreams and make one’s mark in a world that rewards conformity and compromise.

Reeling from the distribution woes of their previous film, Platts-Mills and St John put this one out themselves. Around the same time, as well as being made a governor of the BFI, the director established the Prodigal Trust, providing access for schoolchildren to video production equipment. He also formed Massive Videos in London, which offered film-making experience to trainees, many of whom were disadvantaged, and worked with prisoners in Glasgow. For most of his later life he worked relentlessly with colleges and community organisations.

He directed two other features: Hero (1982), in which Glaswegian youths act out an ancient Scottish fable entirely in Gaelic, and Zohra: A Moroccan Fairy Tale (2010), also made with non-professional actors, which emerged from his time in Asilah, Morocco, where he had lived and worked since 2000. It was there that he founded the Ecole de Cinéma de Larache to provide training for youngsters.

Though Platts-Mills did not go on to have the sort of career that admirers of Bronco Bullfrog had predicted, what he did instead was arguably more valuable. He extended the practices by which that debut was conceived into a lifelong philosophy, and became a facilitator for young people to express themselves. He once compared his attempts at challenging the structure of the film industry to “a bus conductor trying to take over London Transport”. If so, he had the decency to bring other less fortunate souls along with him for the ride.

He is survived by his partner, Catriona Guinness, and by his children, Ruby and Roland, from an earlier relationship, with Sara Wallace. A marriage to Caroline Younger ended in divorce.

• Barney Platts-Mills, film director, born 15 October 1944; died 5 October 2021