So, in the 20 years that have passed, what did happen to Gregory?

Director Bill Forsyth was conscious of the enormous affection with which his film Gregory's Girl was received on its release in 1980 and in which it is held even now, when he began the process of writing and directing Gregory’s Two Girls.

"We were aware of the dangers of even contemplating recreating Gregory," says Forsyth. "We did not approach it as a sequel - not after all these years - but as another film with the same character. So we virtually started over again, with a clean slate.

"We decided to eavesdrop on Gregory's life and to ask: where is he now? What is he up to? The original character was adolescent and awkward, almost in a pantomime way, and we might have made the mistake of going overboard in trying to ingratiate the new character with the audience. We avoided that not least by the sheer acting instinct of John Gordon-Sinclair."

Forsyth was delighted when Gordon-Sinclair agreed to reprise his leading role in the original film. "Having John play Gregory again was like an anchor - his persona would always give the character its integrity," says Forsyth.

"As it happens, John plays Greg as a solid, grown-up person, not as someone pretending to be a teenager. He still has that innocence, but he's a brand new character in the same skin.

"The closest we came to parodying the original film was in the shower scene. Greg feels he must be super-clean before going out on a date, so he showers several times. In that respect, some things don't change in a human being, whether they're 16 or 35."

Both director and leading actor recognised the dramatic potential which the 20-year age difference presented. "One of the main comic and dramatic starting points is that Greg hasn't travelled, geographically, at all in his life," says Forsyth. "He's now a teacher at the school where he was a pupil. He's a sensitive and liberal individual with a highly developed sense of the outside world. He tries to transmit this to his pupils - but he has no worldly experience. That became a strong story point - how someone may have strong views about the world but they don't know how to relate them to their daily life.

"Greg lives through magazines and television documentaries in a way I suspect a lot of us do nowadays. Thanks to technical advances - another major difference between then and now - we experience the world much more through the media and much less through direct contact."

Says John Gordon-Sinclair, "Gregory teaches his pupils to get involved and try to change the world but when he's confronted with a possibility of doing that himself, he backs off. His pupils force him forward to take action, and in so doing he proves to himself that small people can make a difference - even if it isn't a huge difference."

"Because Gregory has lived a fairly quiet life in terms of outside influences, he's got more direct access to what it's like to be young," says Forsyth. "Perhaps that's why he comes across as a good teacher - he doesn't keep on the railroad tracks of the curriculum. A running gag is that the kids have to put up their hands and say 'Please Sir, you're wandering off English again'."

"Everyone feels very protective towards Gregory," says Gordon-Sinclair. "I know I do, and Bill does. He hasn't moved far from his family home in Cumbernauld, so he's never really left that small-town environment. He may be more complex because he's been to university and he knows more, but he's still very naive, especially in the way he deals with women."

Says Forsyth, "Gregory has a lot of growing up to do. He's involved with Frances, a 16-year-old pupil who's bright and attractive - just the sort of girl the original Gregory would have been attracted to when he was 16. And although he's 35, in his head he still has the same adolescent yearnings for her. It's a real situation and we try to deal with it in a real way."

Forsyth was acutely aware of the delicacy required in handling this dramatic theme. He says, "Because John is quite unique as an actor he can walk the fine tightrope of the teacher having a crush on a pupil and at no stage do we condemn him because we can see how hard he's working to deal with his feelings for Frances. How he suffers as much as he gains pleasure from it."

Forsyth describes Carly McKinnon, who plays Frances, as "a find-and-a-half. Carly plays a wise 16-year-old, which she is, but there's still that fresh, youthful thing about her. She was a complete natural and very instinctive, with a quick response to any direction or change of style. She was wonderful to work with."

Carly, like her fellow 'activist' Hugh, were selected from youth theatre groups around the west of Scotland. "They're just quite natural performers," says Forsyth. "That's another change of the last 20 years. Young people have become so used to being in front of cameras and operating them, and they're used to giving some realness back."

This realness was put to good use in a scene where Frances and Doug try to persuade Greg to break the law with them. "Their idealism is fired up and they are unwilling to compromise," says Forsyth. "The two young actors played it with such directness it paid off."

Says Carly McKinnon, of tackling her schoolgirl character, "At first you think, she's a teenage girl and there's not a lot you can do. But I think Frances is a lot like me - headstrong and interested in many things." It is Frances' fresh, untested idealism which forces Gregory into the position of being a whistle-blower over certain activities at Rowan's factory.

"We get some fun out of the idea that Gregory might share Frances’ ideas, but he's longer in the tooth," says Forsyth, "pitting finely-tuned youthful idealism against the slightly more cynical adult view about how to change the world."

Gregory's other 'girl' is the female teacher Bel, a character Forsyth describes as "a more realistic option for Greg in terms of a partner. I don't think Bel scares him, more that he hasn't noticed her, because she's become his friend. It's a take that many men have - if a woman is your friend, then she can't also be your lover. They've known each other for eight years and they've never touched - a situation a lot of people will relate to."

About casting Maria Doyle Kennedy as Bel, he says, "I tend to be obvious in the way I cast my films. I don't look for actors and mould them to the characters. I look for actors who are like the characters. Maria had all the qualities I wanted in Bel - an intelligence, openness, directness and warmth. She's a singer, too - I think female singers can't help but be sexy. Maria is a very strong woman, and having a strong woman was a lot of fun."

"Bel is supposed to be gorgeous and a bit more mature, as opposed to Frances who's gorgeous and young," says Doyle Kennedy. "It's important that both women are gorgeous, whatever their age, for the audience to understand why Gregory likes them both. Gregory’s Two Girls is a very funny film but there's a lot of social comment, too. It taps into a commonly held myth that says we're not as beautiful or as treasured as we get older, and that youth always wins the day. I really don't think that's true, and if I can show that there's life after school uniform and long legs, I'll be happy."

When casting Fraser Rowan, Greg's old schoolmate turned millionaire entrepreneur, Forsyth says he faced a challenge: "Fraser is an unsympathetic character - but the film demands that he's liked by the audience. That's easy to do if it's a genre piece - you create the nice baddie. But Fraser is a complex man: he's active and committed to his own goals. He's on the other side of the fence to Greg in terms of moral issues. But when they're together he and Greg are like adolescents again. It demanded a more subtle performance, and so I was very pleased when Dougray Scott was interested in the part. We built the character up scene by scene, asking the question: in this bit will Fraser show his nice or his nasty side? Working with Dougray was a joy."

Scott describes Fraser, who started from the same base as Greg but has manipulated a very different course in life, as "the most unpleasant man in the world. Like a lot of people with money he tries to buy friendship and he showers Greg with electronic toys and gadgets, because he doesn't know what else to do."

Adds Forsyth, "In the original film Greg is someone who's inept with gadgets, so that is one consistent thread in his life. Fraser's gifts, such as the mobile phone, binoculars, digital camera, are things which are still anathema to Greg but which are forced on him."

"Actually, I like Fraser," says Scott. "He's a lonely, complex character who argues that his factory may be producing instruments of torture for the Third World, but that he also gives money to African charities. Instead of preaching in a classroom about Third World hunger and poverty, he's made a real difference to these people's lives." He adds, "I've always wanted to work with Bill Forsyth. He's a genius and a maverick, and he writes in such an unobvious way and with a great heart. I think this film has got all of that."

Martin Schwab, who plays human rights acitivist Dimitri, is a Dutchman who hails from Indonesia. Says Forsyth, "Martin had to come into the midst of these British and Scottish actors who were working in their own language and deal with that. But part of the reason he was perfect casting was that he brings this strange exotic element to the film. Martin worked hard at not losing his exotic edge. He knew what he was doing, and he kept the eccentricity going."

In researching the film, John Gordon Sinclair met someone who works as an environmental activist - "a real Dimitri, whose life was about smuggling himself into arms conventions and getting information. Like James Bond but without the tuxedo and the glamour. I found his story very humbling. Once you've met someone who's been involved on the scene like that, you wonder whether you've gone far enough with the film. Then again, I think a point Bill's trying to make is that arms dealers and manufacturers of electric batons don't work out of mysterious complexes in the middle of nowhere - they live next door."

Says Forsyth, "Dimitri is an Asian human rights activist who's suffered torture and imprisonment at the hands of his government. The sort of guy Gregory has only seen in TV documentaries, and then finds him ringing his doorbell.

"I think that's another big change of the intervening years - how we now live our lives, mediated through television and magazines. You can watch a flood on the news and be moved, and even be moved enough to pledge £50 and believe it's taken care of. But in a human sense we're not confronted with these things. I do feel people have to grapple with who they are and how they fit into this global informational network. Are we just consumers of facts? as Greg says in the film. Or are we going to do something about these facts?"

Kevin Anderson who plays Jon "the thinking, feeling Yank" says, "I think my character helps Greg take that turn out of his comfortable little world. He's been preaching to the kids for years, and then meeting this person who's intimately aware of the issues enthuses him, and that enthusiasm carries through the film."

Some things had to stay the same when shooting Gregory’s Two Girls, such as certain key locations from the first film, like the school where Gregory teaches. "It was an important story point that Gregory was back in his old school," says Forsyth. "Knowing some people have such a strong attachment to the original film, there was no way we could cheat and use another school. When we went back, the headmistress made us quite welcome. In fact, she'd been at the school during the first film - as a trainee teacher."

And when Gregory makes a secret assignation with Frances, he arranges to meet her at the same park, under the same tree as in the original film. "He does that because he's a bit simple-minded," says Forsyth. "But actually when we went back to the park and looked for a tree to shoot the scene under, it turned out to be the same tree from the first film - although we didn't intend it to be."

On creating the look of Gregory’s Two Girls, John de Borman, Director of Photography says: "I like to create a different style and look for each film, to create its reality. Gregory’s Two Girls is probably the closest thing to The Full Monty I've done. We didn't want the 'comedy look'. We kept it very natural, and it has more of a 'French cinema look' which suits Bill's gentle style and classical approach to narrative."

Producer Christopher Young, who did not work on the original film, says: "It is unusual to go back to a film that was so much part of people's imaginations. Most of my friends and family saw Gregory's Girl and when Gregory’s Two Girls comes out, they'll go and see it because they're curious to see what happened to Gregory. It's definitely going to appeal to a sophisticated audience."

As for himself, Bill Forsyth says, "When the original film came out I was troubled that people assessed it as a comedy, a light piece of work, perhaps because it was about kids. To my mind there were layers there. I suppose, 20 years on, the layers are still there but they're darker.

"I have an awkward relationship with the cinema business, especially the American product we're subject to. If I had to describe myself as a filmmaker, I'd say that if cinema is a supermarket, then my films would be in the organic vegetable tray – not your regular product, but I hope there's more sustenance to them than in the can on the shelf.

"You don't need to have enjoyed or experienced Gregory's Girl to enjoy Gregory’s Two Girls. Anyone can sit down and enjoy this film on its own terms."