Started the week with a charity preview screening of Godsend. A friend of mine is responsible for an organization called YCTV. It's based in West London and was set up ten years ago to provide young people in the area with the opportunity of learning to work in television and film. They've got a great building, which runs as a kind of youth club for young hopefuls, and they hold workshops and courses throughout the year. The major broadcasters financially support it, but they rely on individual donations and charity events as a way of additional fundraising. We gave them the film and worked with them to get an invited audience, whom we then charged a lot of money for the privilege of seeing it.

My friend Molly Dineen did a quick interview with me, which the YCTV kids filmed. I introduced the film and then did a Q&A afterwards, with one of the kids acting as interviewer. I'm attracted to this charity because I've seen it grow from nothing to what it is now - a thriving centre of creative activity, which genuinely acts as an alternative to hanging out on the street corner and offers unique opportunities. As part of the process they invite professionals to do classes / workshops. The thing you realise is, they're not listening to you because of who you are, but rather because of what you have to say.

It's a salutary experience, thoughts and ideas that you've been working on and thinking about, when spoken out loud to a crowd of young people sometimes have no resonance. You have to be interesting, you have to be inventive... they'll tell you immediately whether or not you're on track. Teaching is part of the job of being a director, good for you and good for them. It keeps you sharp.

Opening up ideas and exposing your thoughts in this way is what directors do on a regular basis. Most often we put it into our work. Publication is what we want, yet sometimes the result of that publication is something we don't expect. For example Godsend opens this week in the UK and therefore I've undergone the process of criticism.

I've lived with this for so long, both in the theatre and film industries, that I've developed a defence mechanism. The press' expectation is often different from what you want to deliver. They will write what they want, it's their privilege to do so, any complaints about that process are churlish, that's the business... get on with it! If you're going to make something and have something to say, then by default someone in turn is going to write about it and say you don't. You naturally want the right to reply, but you can't, so you have to do it through your work.

Original stories are the most difficult to find. I'd rather do something that didn't work but was original, as opposed to something I'd seen many times before and just follows a formula. The catalyst for the horror in Godsend is something I hadn't seen before - here was an example of science fiction, which very soon will be science fact.

Genetic engineering is a subject which has been looked at before in movies. However, what is new here is that this subject is placed within such a domestic context. This is the classic "what if" story... What if this happened to you, what decision would you make? The movie is the story of one family making a choice and suffering the consequences of that choice. The terror is supplied not by a ghost or a freaky alien but by something in your own house... Horror in daylight is much more disturbing then horror in darkness.

In fact, the movie photographically moves in the opposite way to most horror films. Our film starts in the dark, frenetic world of a downtown American city and moves towards the pastoral, bucolic environment of the countryside. We move from dark to light - most horror films move from light to dark. The audience's imagination is infected by the atmosphere of the movie, so that everyday environments suddenly become truly terrible.

The trick is to let the audience do most of the work, set up the world, and then by sometimes doing nothing one is doing a tremendous amount. An audience's imagination is greater then anything a filmmaker can realize. My job was to make the slightest thing have the biggest possible consequences.

So I did the charity event, then did a quick appearance on BBC breakfast television where I rattled on about cloning. I followed on from the father of Nick Berg, who was the previous guest to me. He'd been talking about his son and I found it tremendously hard to be in anyway entertaining or relevant after listening to him. I congratulated him afterwards in the green room; it takes a lot of courage to be that public with your grief.

As I've said before in these diaries, when you get down to it everything is always dependent on the actor. The difficult thing about the film business is that the actor you often think makes most sense for the role doesn't necessarily excite the finance. Trying to find a balance between these two is a constant struggle in the casting of a film.

I'd just come out of a meeting with the financiers to the next movie and was wandering down Dean Street when I bumped into an actor I'd originally worked with at the RSC. He's an extraordinary talent and now doing very well in movies. He was standing with the writer and director Terry George, who is in the process of editing his new film. So there we were, all standing on the street corner, moaning and groaning like you do. Complaining about how there is no money around, and it occurred to me that the best results always come about when you're true to your instincts. When your intention is clear and you don't compromise for the sake of what you think the market wants.

Years ago I cast the actor I was now standing with, against everyone's advice. They said he was difficult, unruly, and wouldn't fit in... Well he did, he grew up, and is a great natural talent. Casting is sometimes like that, you need to believe in someone against the odds. It made me realise that I was right to stick to my guns in the previous meeting with the financiers. Anyway, they wandered off to see a preview of Fahrenheit 9/11, as it seemed did half the street. I talked earlier about movies that can change lives: this one might change an election result.

More LA video diary again next week.

Nick shot video footage of himself recording a director's commentary for the Godsend DVD:
Watch it here