“I’ve never had any time for Rangers or Celtic, or the whole sectarian thing that surrounds them. I was always a Third Lanark man, but they don’t exist anymore,” declares Gilles MacKinnon. Though the exploits of his now defunct team are lost to all but the most anal of football historians, its hardly surprising that the subject of the beautiful game (or what passes for it in Scotland) has come up. The Scottish film director has already explored the related sectarian divisions during the 1960s that defined his native Glasgow in his acclaimed 1996 feature Small Faces, while his latest film Pure explores the fortunes and misfortunes of downtrodden ten year old Paul (a magnificent performance from newcomer Harry Eden) and his drug-addled mother (Molly Parker) in the grim East London distinct which hosts Upton Park – home of West Ham football club.

Rather surprisingly, given the gritty nature of the film, the club was very co-operative with the project.

“It did take some time for West Ham to come around to the film,” explains MacKinnon, regarding the Hammer’s involvement.

“Obviously, they were nervous given the kind of film that we were making and they did have certain rules. For example in certain scenes, they didn’t want their merchandise to be visible. They were very reasonable, really.”

A gritty and absorbing drama, Pure was written by Leeds based journalist Alison Hume, after her experiences researching a charity that was writing a booklet to help children deal with their parents’ drug addiction. As one might envisage given this background and subject matter, MacKinnon’s film is candid and hardhitting stuff.

From the opening scene where our ten year-old protagonist heats up his mother’s fix in a spoon by way of breakfast in bed, to his sixteen year old mate (Keira Knightley) feeling her baby’s exaggerated inuterine movements following a spot of dragon chasing, Pure often offers moments of desperate sadness and social deprivation.

“When I first read the script,” says MacKinnon, “it was those little moments that grabbed me, and they grabbed me in a very understated way. It meant that I was going to be making a film which didn’t glorify drugs in any way. I didn’t want to make a sexy drugs film. That just isn’t the right way of going about things.”

The director was also keen that his impressive young leading man was somewhat protected from the subject matter.

“We got so lucky with Harry. He just had something. And he was a real West Ham supporter! But he’s dyslexic, so there were difficulties. We had to blow up pages of the script to a huge size, so that he could learn his lines, and we had a dialogue coach working with him, just to get his confidence up. But what really worried me, and what I kept saying to him was – I know you’re on a film set, and it’s exciting, but don’t get that and the subject confused in your mind, because I really didn’t want him to associate the glamour of working in films with drugs. I was really hoping he’d go on, and do something light, but his next role was in a child abuse drama! Still, he’s done Peter Pan since, so I was glad of that.”

Yet the film is far from grim, and instead strongly emphasises the possibilities for redemption.

“It had to be that way,” MacKinnon tells me after the film’s recent Irish premiere at the Dublin International Film Festival. “About ten years ago, I directed the Jimmy McGovern drama Needle, and it has a bleak ending. I couldn’t go through that again. It was a genius script for Needle, but it was hard to switch off at night. I did work for five years as a youth worker in London, and I always say that I learned more about actors, and basic psychology with skinheads in Kilburn, than I ever did on a film set. So that’s part of the reason, I wanted the movie to have hope too. I needed to do a movie about people who can survive this time.”