Paul Laverty: Script-fighting man

The swearing in Sweet Sixteen, writer Paul Laverty's fourth film with Ken Loach, earnt it an 18 certificate. As Fiona Morrow finds, that's just one of the reasons he's hopping mad

Paul Laverty is angry. And he has every right to be. Sweet Sixteen – written by Laverty, directed by Ken Loach – has just been awarded an 18 certificate by the British Board of Film Classification. Not that it's much of a prize: such are the unfathomable vagaries of the BBFC's judgement, that a film about teenagers in the deprived west of Scotland is now off-limits to teenagers. Why? Because – surprise, surprise – these same kids are prone to swearing. It's a stupid decision – not least because it comes on the back of the new, relaxed 12A classification – and one that surely calls into question the usefulness of the board's opinion on any level.

"I'm furious about it," spits Laverty. "It's nothing but censorship and class prejudice. It's OK to give Black Hawk Down a 15, with its exploding body parts and virulent racism, but we get an 18 because of [and he quotes] 'the aggressive use of the c-word'.

"It's like, this is an aggressive word which really gets up the nose of polite society. Just like it would get up her nose if you tried to use it in front of your working-class granny, but," he notes with exasperation, "the kids on the street corners use it all the time."

For Laverty, it's all about authenticity: "It comes down to the way we approach the film. We let the kids speak the way they actually speak. Can you imagine saying to the kids, 'OK, you can swear and curse – just don't say that word'?" He has registered his protest by letter. Today, he's happy to make it more symbolic. "I'd just like to stick two fingers up to the BBFC and their upper-crust British sensibilities."

Laverty may be angry, but he's gentle with it; at times, I have to strain to hear him. (You can see how he would work well with the notoriously reticent Loach.) He speaks quickly and enthusiastically, punctuating his thoughts by rubbing his hands across his shaved head. Though based in Madrid, he has flown down from Scotland this morning, arriving for the interview clutching coffee and a muffin. He offers me a corner of the cake before quickly reducing it to a few crumbs.

His circuitous route into film-making is well known: originally a lawyer, then a charity worker in South America, Laverty's first writing foray became Loach's cross-cultural love story, Carla's Song. Sweet Sixteen is their fourth collaboration – in between was My Name Is Joe and Bread And Roses. It's a career that reeks of conviction; his work is regularly classified by critics as didactic.

Laverty makes no apologies for the emphasis of his work: "Of the films we see, 99.9 per cent are about white, rich, articulate, middle-class, well-educated people," he counters, before adding, with a smile: "I'm generalising, but in general it's true. Yet people seem to think that with My Name Is Joe and Sweet Sixteen, we've exhausted the entire spectrum of the working-class population. The implication is that these experiences are somehow narrower or less three-dimensional. You don't hear people saying it about Woody Allen's films."

I mention that some have described Sweet Sixteen (which centres on 15-year-old Liam and his struggle to escape the local drug culture) as "Mean Streets set in Scotland". Laverty's face clouds. "That kind of thing never even crosses my mind," he says, a trace of acid creeping into his genial voice. (His instant change of mood reminds me of his opening gambit: "Are you a film critic, Fiona?" – the directness of which had surprised me. Would he rather I weren't?) "I think there's so much live, raw material," he continues, slightly frostily. "And so many choices in front of you already, that the very last thing I'd think about is making some kind of film reference."

I feel the need to re-establish my credentials. I know a little about the geography of the film, I say, as the flicker of a frown begins to appear on his brow, because my dad's from Glasgow and my grandparents lived in Gourock. A little jokey aside about swimming in the open-air pool (filled with the freezing waters of the Clyde), and we are – as Dad would say – singing from the same hymn sheet again.

I ask whether he thinks critics choose to talk about the nuts and bolts of film-making in order to avoid having to engage with the issues. He nods: "They start going on about melodrama, and I have to wonder why that is. Do they think I'm exaggerating? In comparison to some of the stories I found while researching Sweet Sixteen, the one I told is a picnic."

The defensiveness is understandable: Laverty and Loach are coming from a political position increasingly marginalised; always vehemently anti-capitalist, that now pits them against the modern incarnation of the Labour movement. too. I ask him whether it was easier to protest under Thatcher and he laughs: "I think that's a very good question, and certainly I doubt if the Tories would have got away with some of the things Blair and Straw are up to – they would have suffered a bigger backlash.

"Tony Blair is quintessentially a man of business. The sooner we recognise him for what he is... and the situation with Iraq is demonstrating his sycophancy; Tony Doormat in thrall to Mr Picklechops. I'm amazed to see what an arse-kisser Blair is."

Though he believes his work is simply "chipping in from the sidelines", Laverty is absolutely clear about his motivation for continuing to take part in the argument. "I'll never forget my time in South America and what I saw, and the truth of what Bush's father was doing there," he recalls, sombrely. "I'll never forget talking to people whose children were mutilated or murdered. When you actually see it, it's something you never, ever forget. And so, when you hear Bush Jr using the same language – all the talk about human rights – it takes you straight back there. That's why it's important to re-examine the historical record."

The forthcoming compilation film, 9.11.01 sees Loach and Laverty doing just that. In it, different film-makers each present a film that is nine minutes, 11 seconds and one frame in length, responding to September 11; the British duo chose to remember that date in 1973, when Pinochet illegally overthrew Allende in Chile. "Vladimir Vega [the Chilean actor who starred in Ladybird Ladybird and Carla's Song] remembers his Tuesday," explains Laverty. "He remembers his friends who were murdered, and he remembers Kissinger and Pinochet talking about human rights..."

Some people, no doubt, will call it didactic. Alexander Walker in the London Evening Standard said that it "brings shame on this country". Me? I'm not a good enough film critic; I'll take conviction every time.

'Sweet Sixteen' is released on 4 October

'I was so terrified, I didn't need to act'

Many of the stars of Sweet Sixteen were born in Greenock, where the film is set. Martin Compston, who plays beleaguered hero Liam, had never acted before and is sweetly modest about his stardom. He plays for Greenock Morton FC and hopes to make football rather than acting his career. But if that doesn't work out he confesses to a secret desire to become an accountant – possibly the first actor to nurse such an ambition.

"This will be something to look back on and show the grandweans on video," he shrugs. Although he had seen a couple of Loach's films before and admired them (particularly the football scene in Kes) he says that he didn't really appreciate the significance of what he was doing at first.

"I didn't feel too well when filming was scheduled to start and wanted to phone in sick for the first few days. I didn't understand that you can't do that with a tight filming schedule. I worked 8am to 7pm most days and just wanted to sleep when I got home. Two weeks into the filming it suddenly clicked what it was all about."

He says the kind of violence in the film and the widespread heroin use are part of everyday life in Greenock. "It can get like Braveheart round here with one side running at the other. It used to be fists but now it's guns."

Loach always films in sequence and gives the actors only as much script as they need to see for the following day's filming. At this point suspense is mounting about how things are going to end for Liam, but no one who knows is prepared to divulge a thing. "There was a knife scene and Ken prepped me for days about how I would have to use the knife. The scene turned out differently from the way I had thought it was going to go; I was so terrified, I didn't need to act."

He says he loved working with Loach and his team. Egos are absent, along with directorial cliches such as "cut". "Ken is a workaholic," says Compston. "He never says 'cut'; he says, 'That was so excellent we'll just do it one more time', and that usually means three more times. He can go on for hours. I loved playing Liam because so many of my friends are just like him. I don't know if I could act something different from me, like gay or romantic."