Jeffrey Harrison arrived in LA in the 80s as an aspiring actor, and soon got into regular sperm donating for $25 a pop at California Cyrobank. Now 52, estranged from his own divorced parents, he exists somewhere between Iggy Pop and Ace Ventura, a bong-smoking conspiracy theorist living with a load of animals in a broken-down RV on Venice Beach with many, many children.

JoEllen grew up with two lesbian mothers who split when she was six; when she was 12, one of them told her about a website that allows children of sperm donors to find their donor siblings and parents.

In his new documentary Donor Unknown, British director Jerry Rothwell follows JoEllen Marsh – now 20 – as she sets off to California to meet the anonymous sperm donor who created her (guess who that is). I spoke to Rothwell, who was previously responsible for Heavy Load, the documentary about the Brighton punk band with learning disabilities. He's a good man and this is a great film.

VICE: I read that this film came about after Jeffrey contacted your producer about another sperm donation documentary she'd worked on.
Jerry: Well my producer was doing a drama for the BBC and as part of the research she put an inquiry out online to find out people's experiences, and Jeffery called her up in the middle of the night. He had a sperm donor Google Alert which he'd look at in his local internet café. I think he was just interested in those issues. And they talked for a year, and she told me "I keep getting phoned by this guy in the middle of the night by this guy with 14 kids."

So obviously it's something that had been playing on his mind for a few years.
Well at that point he had come forward to the kids, and had met some, not the ones in the film. In the States, if you're an unknown donor, what you consent to is that when the child is 18 they can write you a letter, and it's up to you whether you respond to that or not. And he said, 18 years after donating, he was beginning to think "Where are my letters?" So it was obviously something he had thought about.

So clearly it ended up meaning more to him than just a bit of easy cash.
Yeah. Absolutely. If it didn't mean any more to him than that he wouldn't have come forward.

What were your thoughts after you met him?
My take was that you could see these parallel journeys, with the kids looking for Jeffrey, and Jeffrey seeing the kids. And it seemed to me that Jeffrey was in a situation where he'd kind of run as far away from family as you can possibly go, while this completely different family was coming and claiming him. That was one of the things that interested me. I think if he'd been the classic donor, a medical student who was now comfortably off with two kids, it would have been a different film.

Had you had any prior interest in sperm donation?
Well about 10 years before I'd had radiotherapy treatment and they offer you sperm banking as part of that, in case you become infertile, so there was that sense that "There's a bit of me sitting in a room in Hammersmith somewhere, what does that mean?" That interested me in the issue.

Did working on the film lead you to explore that further?
Yeah it's lead me to want to destroy the sample! I mean they can't use it for anyone else, it's for your own kids, but it made me want to draw a line under it, because who knows what the possibilities are.

I told a friend about the film and her immediate reaction was that if she was in that situation she wouldn't want to know who her donor was as it's just someone wanking for cash and it's meaningless. Whereas I imagine I'd be fascinated to know who was responsible for 50% of my DNA.
Well I think what drove JoEllen to find Jeffrey was that mixture of fascination and curiosity. I think what stops people looking in a lot of cases are the potential stresses it might introduce into the family that they currently have. I think JoEllen was in a situation where her mum was really supportive; there were no issues about it. But I met others for whom it was too difficult to engage with.

Jeffrey was just doing it for cash, but then in the film he also dresses it up as these divine miracles in which he was being asked to be a 'soul-caller.' It's hard to tell if he actually thought that at the time.
Yeah. It is hard to tell. I wouldn't be surprised if he thought that at the time because that's very much Jeffrey's way of thinking. But I guess in the film I play with bouncing that notion of being, as he says 'a soul-caller', against seat covers and diagrams of how to wash your hands afterwards, the clinical environment in which that happens.

Yes, your film introduced me to the word 'masturbatorium'.
Yeah, I think that word is unique to the California Cyrobank.

An interesting moment in the film is where Jeffrey looks at his old donor form, and he explains that while he wrote that he was a dancer, he was actually a Chippendales-type male revue performer. It says something interesting about vanity that even in that anonymous, detached situation you'd still want to make yourself seem more attractive, an idealised version of a father.
I think sperm donation almost uses the language of dating agencies, now even more than then - they ask you what your favourite food is, what you like doing in the evenings, things that are probably irrelevant to genetics. Those forms are reliant on what people say about themselves, just as dating sites are.

Does Jeffery like the film?
Yeah, he does. He feels that it sums up that bit of his life.


Donor Unknown is in UK cinemas June 3. It's showing on More4 on June 28, and is out on DVD July 4.