David Bradley wants to meet in Barnsley. This is where he grew up. It is where Kes, the film that changed his life, was made, and where he still lives. He is waiting for me in the middle of the road as I come out of the station, waving exuberantly. He then drives me a few miles south to the village of Tankersley. It was here, in 1965, that author Barry Hines’s younger brother, Richard, trained a kestrel, homing her in the air-raid shelter at the bottom of Barry’s garden. Richard wanted to call her Kessy; Barry suggested Kes.

Bradley wants to talk in a pub he likes, which seems a generic suggestion until we get there: the last time he was here, he says, was for Barry Hines’s wake. Hines, who had Alzheimer’s for nine years, died in March, age 76, and is buried at a nearby church. Bradley, now 63, softly spoken and sensitive, has been inextricably linked to Hines and Kes since he was cast, aged 14, in Ken Loach’s 1969 adaptation of Hines’s novel A Kestrel for a Knave. The film, about Billy Casper, a neglected working-class 15-year-old who finds solace training a kestrel, was a gentle drama about harsh circumstances. It was a sensation, winning Bradley a Bafta for most promising newcomer.

Bradley was, he says, an ordinary kid who had failed his 11-plus and went to St Helen’s, a Barnsley secondary modern school. His father was a miner, and Bradley was expected to follow suit, but says he wouldn’t have been able to cope down the pits. Local author Hines didn’t yet know Bradley, but he knew kids just like him. Hines’s father was a miner, and Hines, who had been a teacher at St Helen’s and modelled the school in his book after it, wanted to write about the pig-headedness of disregarding pupils who failed the 11-plus, thus branding them with inferiority complexes. Loach was equally keen to mine the subject on film.

Bradley, who had starred in school pantomimes at St Helen’s, showed off keen improvisational chops in auditions, and was offered the job. The same day, a fortnight before shooting began, he was summoned to Barry Hines’s house to start training the three kestrels to be used in the film. (They were named Freeman, Hardy & Willis, after the shoe shop.) Bradley was paired with Hardy, while Barry and Richard worked with the other two, which was just as well: “Willis was freaking out all the time: it just wouldn’t do anything. We had to reintroduce him back into the wild.”

Bradley with Barry Hines during the filming of Kes. Photograph: Allstar/Woodfall Film Productions

In striving for authenticity, Loach was as unpredictable as Willis. “He would play tricks to see if he could get a reaction,” says Bradley. In one scene, Bradley runs down a street, chased by a barking dog: he is convinced Loach had someone hiding who “threw the dog into the middle of the road”. For the famous sequence in which Bradley and other schoolboys are caned, they had been assured Loach would call “cut” just before they were struck – he didn’t. “You can’t imitate that expression, the point at which the cane strikes the hand,” Loach later explained. “So we just caned them, really.”

To elicit a realistic emotional response for the film’s bleak climax, in which Billy’s self-loathing brother Jud (Freddie Fletcher) kills Kes, Loach approached Fletcher and Bradley in the lunch queue and told Fletcher to go off with Richard Hines and slaughter Hardy for the required corpse. Bradley says he wasn’t convinced – “I just couldn’t believe these nice people could be so cruel” – and after shooting the scene was reunited with Hardy (the one on camera had died from natural causes). “I said to them: ‘I knew you wouldn’t kill him! I knew you wouldn’t!’”

After Kes, Bradley changed his professional name to Dai (because of the other David Bradley, last seen in Game of Thrones), got some TV work, enjoyed a spell with the National Theatre (including the lead in Equus), and on film appeared in Zulu Dawn and 1979’s All Quiet on the Western Front. After that though, work dried up somewhat. He bought a church and spent three years part-converting it into a home, but his co-investor didn’t come up with the other 50%. Meanwhile, a play he was doing in the US came to nothing when the producer didn’t arrange for him to get a green card. He came home, and reluctantly sold the church.

He speaks with great affection about Kes – the tie has not been cut. In 2009, he told a BBC TV crew that every couple of years he revisits the woods filmed in Kes, as they remind him of making the film. Does he feel emotionally attached to it? He pauses for some time. “I wouldn’t say ... I don’t often go now, I try to go at least once a year, because the wood which Billy used to walk through to the old ruined manor house was absolutely fantastic when I was a young lad. It was as you saw it in the film, a canopy of green dappled sunlight.”

He appears at public screenings of Kes, but can’t watch the last 20 minutes as it upsets him too much. “I have to apologise to audiences,” he says. “I say to them: ‘Please excuse me if you see this shadow walking out at the end; it’s just too much to stay behind.’”

Bradley in Kes. Photograph: Alamy Stock Photo

I ask about the site he runs, called Kes: Billy Casper, which features his CV, a guestbook and a detailed rundown of the film’s locations. “It was prompted by the fans,” he says. “But I get so bored of it. There’s a fan section where they’re invited to write to me, and there are hundreds of these little promos for various types of pills. And I just get so bored of erasing those all the time.” Spam? “Yes, offering legal-high-type things. I erase a month’s worth and then another couple of months’ worth comes within a week, and I think: ‘God, why did I invite the fans to write to me.’”

I ask if he stays in touch with anyone from the film. “We try to see each other once a year if possible, just for half an hour, to say hello,” he says of Loach, and then, talking about Barry Hines, comes a reveal. Bradley had got back in touch “because I’d penned a sequel to Kes”, he says, matter of factly. What? He wrote a sequel? A book or a screenplay? “I’d loved for it to have been both. But I didn’t think that I could go through with it without Barry’s approval.” He says that he’s written a few things over the years, including a couple of TV scripts – one called Shake, Rattle and Roll based on his own experiences in the World Backgammon Championships – that didn’t work out.

His Kes sequel came about because someone told him they had funding and an idea for a sequel, but Bradley didn’t like the idea and besides, the money never materialised. “I discovered that he was wanted by the police on three different continents,” he says of the financer. “I tend to commit myself to projects without any kind of financial insurance. And I’m the one that gets burned.” So he wrote his own sequel, in which Billy runs away to London and gets into trouble, sniffing glue, washing car windscreens at traffic lights, but is adopted by a couple and ends up converting a narrowboat. Bradley never showed it to Hines. “He wasn’t well enough. I didn’t even tell his wife. I thought it would upset her.”

He drives me back to the train station, pointing out the church where Hines is buried. I think of an old Loach interview in which he said he cast Bradley because he was vulnerable, open and true. He still is. “I know I’ve had a chequered career, a bit of a rollercoaster. But then that’s because of, I guess, my appearance?” he says, and I’m not quite sure what he means.

“Well, I’m not the boy-next-door type,” he says. “I’m not the macho, martial arts type. I’m just an ordinary chap. An amiable guy.”

We talk about his recent work – a bit-part in the Jason Statham film Hummingbird, and an appearance in Holby City. I ask him if he’s still hoping for something to happen with his Kes sequel. “I’m not pursuing it at the present,” he says, wistfully. “The moment is gone. Sometimes I wonder if there were moments when things should happen. And if they don’t happen … you have to let them go.”