What first drew you to filming this story?

What I was really interested in was a how a group of people were trying to find a new set of relationships, brought about by technology - the internet, but also by the technology of reproduction. There’s a very a tight story around wonder and the offspring that come about because of [Jeffrey’s] donations.

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The film raises a lot of questions about identity, is this a theme that particularly interests you?

The question of how people define themselves is maybe something I’m interested in, and there’s also something about masculinity which interests me. I was interested in Jeffrey as much as I was interested in the children and the idea of this man who’d run as far away from family as you could go, who was suddenly confronted by a kind of family and what that meant.

How much do you identify with Jeffrey and how much do you hope the audience will identify with him?

[laughs] Well I think everyone must identify at some level with getting into a van and heading off to the West Coast! There are certainly things about Jeffrey’s experience that I like and recognise and I think a lot of people recognise, and I think his kids really recognise themselves in him. I think the task of a documentary is interesting because you portray someone from the outside, but you can also portray to a certain extent their thoughts and what motivates them. So you’re seeing them how others see them, but you’re also trying to see them as they see themselves; and in Jeffrey those two things play off each other, because other people have strong opinions about him. You hopefully get to learn more about him and empathise with him.

Do you think there’s a danger of some people writing Jeffrey off as an eccentric old hippy?

People respond to him differently, some people are really irritated by him at least at the beginning. I think there was one review that said, “If you don’t like Californian feelings-speak, vast swathes of this film are going to turn you off.” I think what’s interesting is I’m not agreeing with Jeffrey necessarily about his view on the world, but I’m trying to show it in a way which gives him enough credit as possible to explain it.

Do you think a film like The Kids Are Alright has opened the way to making people more interested in contemporary biological issues?

I haven’t seen The Kids Are Alright, but I think biomedical science is the thing that’s most going to change our world in our lifetimes. I think it’s really going to change our sense of who we are. So I think there is going to be much more discussion about what that means, because our understanding of it really lags behind the science, and our duty to society to think through the ethical issues of it are way behind the science of it.

The film seems to question the morality of sperm banks like the Cryobank, do you think there should be more regulation?

I think the situation in the UK is really different, it’s much more regulated. America being America it’s left much more up to commercial forces. I think the California Cryobank is pretty responsible in what it does on the whole but its primary concern is not children. Its primary concern is about enabling people to get pregnant, so inevitably it’s not prioritising the needs of the kids once they’re born and I think that is a problem. The way the UK has gone, which is to say that if you donate sperm or an egg you need to be willing to be contacted by your offspring, I think is the right way of going.

How has being a British filmmaker impacted this documentary?

Partly it’s quite difficult. The film I made before, Heavy Load [Ed – documentary following the rise of a disabled punk band], was about a bunch of people who lived ten miles away from me, whereas in this film they live 4,000 miles away which means a really different kind of filming. You’re trying to get to know someone really quickly on the same day that you’re filming with them and especially with an intimate story like this, that gets quite difficult. But at the same time to be filming a story about the States, it’s interesting to be an outsider, because you see things that people within the culture don’t see. In some ways it is a film about America, and it’s about American ideas about family and connections.

What’s your next project?

It’s going to be called Town of Runners, and it’s about a village in Ethiopia that has produced a lot of world champion long distance runners, it’s about two girls in that village who at the start of the film are 13 and who want to be runners. I’ve been filming them since 2008.

Donor Unknown: Adventures in the Sperm Trade is due to be broadcast 28 June on More4. You can also catch the film in theatres at Picadilly Circus and London ICA until 16 June, more details of which can be found here.