Farah Nabulsi was at home in west London when she found out her film The Present had been nominated for the Oscar for best live action short. She’d persuaded her teenage sons to stay home and watch the announcement. When she heard her name, she jumped up on the table. Her eldest looked at her as if she’d gone mad. He’d got it into his head that this was the actual ceremony and she had lost. “He was like, ‘Why are you so happy? They didn’t pick you.’ He killed the moment.”

The film is Nabulsi’s directing debut, a powerful 20-minute piece of humanist cinema about a Palestinian man, Yusef (Saleh Bakri), who wants to surprise his wife with a fridge as an anniversary gift. He takes the couple’s young daughter, Yasmine (Mariam Kanj), shopping. But their big day out is ruined by two encounters with Israeli soldiers at a checkpoint. Yasmine is a witness to her dad’s humiliation – she tugs on his sleeve, reminding him to bite his tongue, to swallow the soldiers’ insults. It is a study of injustice that – like the best shorts – doesn’t try to cram too much in.

In her late 30s, she switched her career after working in the City as a stockbroker, then starting a children’s entertainment business. At the height of the dotcom boom she traded biotech and internet shares at a boutique investment bank and later JP Morgan. “I’ve always had a mathematical brain,” she explains with a shrug. “I loved biology and maths, so I went off in that direction. I thought that’s what I wanted to do. I wanted to be a strong, independent woman.”

Most days she’d be at her desk at 6.30am for the morning call and often stayed late into the evening for the US market. The hours were long but she enjoyed the travel, the money and, most of all, learning about new technology. Then there was the adrenaline rush. “I loved it. It was exhausting but I was good at it.”

Nabulsi didn’t have a horrible time as a woman in testosterone-heavy banking. “I never felt like going out and drinking till some stupid hour,” she explains. “And I really can’t say that it affected me on a very deep level where I was my miserable. … I could tell you a whole bunch of stories, but we won’t go there.

“People ask me about being a female film-maker, and I’m like, ‘Listen if you’ve been in a bank dealing with the male of the species then: film-making? Bring it on. I can handle that.’”

Nabulsi was born in London to Palestinian parents. Her father, a Palestinian born in Egypt, came to the UK to study for a PhD in civil engineering. Her mother arrived via Kuwait when her family left Palestine following the Arab-Israeli war in 1967. “I get my rebelliousness from her,” says Nabulsi. We’re talking on a video call; in her box-room study there’s a picture on the wall of a crouching lion painted by her mother.

Growing up, her parents were not political but they never let the children forget their roots. “We weren’t the kind of family where it was like…” She puts on a hushed voice. “‘… Just belong. Don’t tell anyone where we’re from.’ That can happen from trauma.” But family holidays to Palestine stopped after the first intifada in 1987.

Seven years ago, she went back for the first time in 25 years. It was life-changing. “That first trip was everything,” she says, and the words come out in a rush: “There’s 100 Israeli checkpoints all over the West Bank. This is not in Israel.” Her hands hang in the air at the indescribability of it. “This is in the West Bank. And there’s the wall that separates families and separates people from their work, from their lands, from their schools. You’ve got these illegal settlements, illegal by international law.”

She talks about the separate licence plate system, separate roads, and the military policing of Palestinians: “I’m sitting with a mum whose 13-year-old child was taken away by military in the middle of the night. You can’t even begin to fathom it. I was blown away because I thought I’d understood. But there’s just no comparison when you go.”

She came back traumatised. “It almost verged on depression.” To process the experience, she began writing, first three short-film scripts, which she produced. After she wrote The Present, a few people suggested she direct. “I definitely felt impostor syndrome, but I thought, if ever I’m going to direct, it’s going to be this film, because I could see it in my mind’s eye, from the actor who would play the lead to what the little girl was wearing.”

There’s an astonishing scene in the film when Yusef passes through an Israeli checkpoint on his way to work. It’s chaos, thousands of men crammed into a narrow subway. A few men bypass the queue by climbing nimbly across the steel bars above. Nabulsi and two cameramen shot the scene documentary-style at the notorious Checkpoint 300, in Bethlehem, surrounded by Palestinian men going to work; they arrive as early as 3am to queue, and during rush hour it can take three hours to cross. I assumed that the fictional checkpoint Yusef was crossing in the film crossed a border. But Nabulsi puts me right, saying that the film’s checkpoint represents the hundred or so checkpoints that do not cross any borders at all. “No! No! This is all in Palestine. Between Palestinian villages, towns, cities. It’s like me saying, ‘You want to go visit your mum who lives in Shoreditch?’ You’re not crossing to France here. But you have to go through a checkpoint. It’s as bizarre as that.

“It’s humiliating and dehumanising standing there. This is not right for any human being. Animals should not be treated like this. This checkpoint has been made for maximum discomfort. You feel that.”

Her first few hours of being a director on set were miserable. The night before, unhappy with her choice for the actor playing the owner of the electrical shop where Yusef buys his fridge, Nabulsi did a last-minute recast. She zipped around gyms at 11pm and finally found a bodybuilder for the part. He agreed to do the film, but overslept the next morning and showed up two hours late. “To be fair to him, he hadn’t realised the scale of it. He thought I was doing a YouTube video or something.”

He’s perfect: a 16-stone teddy bear of a man. Nabulsi says she wanted to show the decency and kindness of ordinary people. “It’s about tearing down the stereotype of how a dark, bearded man is portrayed on the big screen, as the terrorist or whatever. No. This lovely guy is what many bearded big Arab-Palestinians are like.”

I ask her if there are people in the world of film who have been sniffy about her background in banking. “Those thoughts have crossed people’s minds. I’ve definitely had a few film people treat me in a slightly condescending manner initially. And that must’ve been rooted in that idea, she’s a self-proclaimed film-maker but she hasn’t put in the years or been to film school. But I’ve got a thick skin.”

“What’s important is proving to myself that I can do it.I don’t care what others think of me. And that’s probably why I’ve been able to do what I’ve done, because it really was tunnel vision..”

Does she have any regrets about her years in banking, not getting into film earlier? “No. I don’t wish I’d started in my 20s. All of the skill-sets and experiences and thick skin and organisational skills, having some funds. And having had kids; I think being in the film world with very young children is extremely tough. That entire rite of passage brought me to this moment. I don’t want to reverse time. I’ve arrived in the place where I’m supposed to be. I wouldn’t have it any other way.”

• The Present is nominated for an Oscar and a Bafta. The Baftas take place on 10-11 April; the Oscars are on 25 April.

• This article was amended on 7 April 2021 to add text clarifying that the fictional checkpoints depicted in The Present are not border crossings.