Film: Andrea Arnold interview

"We saw a lot of girls who were supposed to be between 14 and 15 and seemed to have gone right through the stage of being a teenager to very grown up and very mature young women. But we also saw girls of 19 who seemed very young, so it was a matter of finding the right girl, not just the right age," recalls Arnold, whose search began by scouring Spotlight for trained actresses, then widened to youth clubs, then to approaching girls in the area where she planned to shoot her film, before the hunt ended at Tilbury Town station.

Another stumbling block was that the girl had to be able to dance, because hip-hop is teenager Mia's only obvious talent, and her main form of unguarded self-expression. The scenes where Jarvis is shown moving to an unheard beat are both awkward and poignant, winning the film a jury prize at Cannes earlier this summer.

"We were keen to find someone who could dance; not so much dance professionally as someone with a passion for dance and who could really project their personality through dancing. We saw some really fantastic dancers. Then when we found Katie she was right in every way – except she couldn't dance," laughs Arnold.

"In fact, she didn't like dancing at all, and when we auditioned her we had to put the camera on the table and creep out the room so she could dance alone and we could watch her later. Which is of course how we first see Mia dance in the film."

As a film, Fish Tank ticks all the boxes of angry social-issue drama, but Arnold films with great sensitivity and feeling for place and atmosphere. Although she's reluctant to go into details about her own life, she concedes that her two acclaimed films Red Road and Fish Tank and her Oscar-winning short Wasp all have elements of autobiography in their austere poetry. For instance, Wasp and Fish Tank feature mothers who barely cope with parental responsibility. "My mum had four kids when she was very young and was a single mum, so she is similar to the film's main character in Wasp," Arnold says. "Now that I am a mother myself, I can appreciate how tough that must have been but people think of council estates as gritty, horrible places. I wanted my film to show how colourful and vibrant life can be there." Brought up in Dartford and now based in Greenwich with her partner Alex and their daughter Coral, Arnold has a knack for discovering novelty in cityscapes without losing authenticity. . Arnold was unfamiliar with Glasgow when she signed up for her debut film, Red Road; "I found what I wanted by getting into my car and just driving around the city."

Arnold, 48, always approaches her movies with one central image already in place, although she won't discuss the one she had in mind for Fish Tank – "It gives too much away." For the Oscar-winning short feature Wasp, where Natalie Press abandons her kids for a drink in a pub, the script proceeded from a mental snapshot of the insect crawling into a child's mouth: on film, an image that is both unsettling and memorable. Arnold's shooting style is also organic. She shoots in sequence, and gives her actors enough pages for the day, rather than a full script. "For Katie I think it was really good," says Arnold, "because she didn't have to take on the idea of the whole film. She just had to deal with every day. A day is possible, whereas if you think about the next six weeks that could be overwhelming."

Arnold left school at 16 and was drawn towards performing herself, first as a dancer and as a member of a roller-skating troupe, and then as a children's television presenter. In the 1980s she was best known as a big sister-style presenter on ITV's Saturday morning show No 73, alongside Sandi Toksvig. But by the mid-Nineties, she'd become bored with co-presenting shows with puppets and cartoons. "I was never that comfortable in front of the camera, it always terrified me," she admits. "The others in No 73 really wanted to be actors, but I was 18 and really I had just fallen into that line of work. I'm surprised I lasted that long really."

She started taking an interest in production and, by the mid-Nineties, found scripting her youth-orientated environmental series A Beetle Called Derek more rewarding, and gradually edged towards directing. She does acknowledge that her experience gives her a rapport with actors: "I'm very aware of their needs, and what kind of help I should be giving them. Which is to say, not too much. You can't flood them with information. When I was working with Kierston (Wareing, who plays Mia's sexy, needy, immature mother] it was mostly "more bitchy" or "not bitchy enough".

Has she ever been tempted to appear in her own films? "Oh God no," she says. "I'm much happier behind the camera. I find it kind of weird that directors want to put themselves in their films. I saw Leaving Las Vegas and Mike Figgis turned up playing one of the thugs and I thought – why do that? It's a distraction from the actual story and I would never want to draw people's eye away from the story of these people. It would feel disrespectful." v

Fish Tank is released 11 September