A British man who went looking for his sperm donor dad was shocked to discover he has 25 half-brothers and sisters in the US.

Oli Benjamin, whose story is being told in a new BBC documentary, was born in 1999 after his mothers decided they wanted to have a child via IVF and embryo transfer.

His mum Jody and her female partner conceived him with an American donor, who remained anonymous, at a clinic in San Francisco, and when Oli turned 18 he began his search for his biological father.

The Londoner, who works in the events industry, eventually found his dad Daley Dunham, but after flying to California to meet his new-found relatives he decided he was “not interested” in having a relationship with his father because they were just “too different”.

Oli found Daley, who no longer wanted to remain anonymous, a few months after he signed up for the US-based Donor Sibling Registry (DSR).

He was contacted by a woman named Jordan who said she was his half-sister. He was stunned when he found out he has 25 American half-brothers and sisters.

Oli, who was diagnosed with Asperger’s as a child and grew up feeling like an outsider, was hoping to establish relationships with Daley, 48, and his half-siblings, but things didn’t go as hoped.

Speaking before the debut of the 25 Siblings and Me documentary, he told the Sunday Times that he had “no interest” in having a relationship with Daley, and his half-siblings are more like cousins to him.

He said: “Genetics are the door to relationships, but they’re not relationships.”

He wanted his first meeting with Daley to be like a scene from a film, but when they met his biological dad “was a bit like, ‘Hi, No 20-whatever’.”

Oli added: “He’d been through it quite a number of times. It’s funny because Daley and I are really not that alike at all. We’re very different people.”

In the documentary, Oli and his half-siblings tell their story. Some reveal they had no idea they were conceived via a sperm donor.

Finding Daley and his half-siblings has brought him peace.

He added: “It’s much better for someone to be made aware of their donor and who their biological family are and choose not to have relationships with them, than to not know and to never meet them and never be able to make that decision for themselves.”

Oli has noticed that he and his half-siblings look similar in certain ways, be he feels he is “quite different” to them.

In a separate interview, he told the Daily Mail it was “scary” meeting his relatives and the group reunion was “difficult” because it was such a large gathering.

He added: “I never saw Daley as a father figure, always like a cousin or an uncle. We aren’t anything alike personality-wise. But I did get his good teeth.

“The trip has shown me that your family are those who stick by you, who you grow up with, who care about you, as opposed to biological status.

“I have also learned to be more accepting of myself. It’s not about getting along with as many people as possible. It’s about getting along with the people that are right for you.

“And I think I have found a few of those [among the siblings], so I am very happy. As far as I’m concerned, it’s a win.”

Oli’s mum Jody, 46, and her now-former partner travelled to San Francisco in 1998 to conceive their son via a method that was not available to them in the UK.

They chose a donor and were adamant that it had to be a man who wanted to remain anonymous to avoid a potential conflict in the future.

Jody, a director who lives in Oxfordshire and also has twins aged nine, carried the egg that her then-partner supplied for IVF.

MIRROR