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Imagine finding out the people you thought were your parents are in fact your aunt and uncle - and that the people you thought were your aunt and uncle, were in fact your parents.

Would you be angry or embrace your new-found relationships? And who would you end up feeling closer to - your biological parents or the people who raised you?

When a couple cannot conceive, IVF and adoption are among the options. But in some cases, members of the Asian community living in the UK have favoured an informal kind of adoption, where one couple gives a baby to another couple in the same extended family to bring up as their own.

It is impossible to know how common this is as few go through the official adoption process, though it seems to have been more widespread in the past.

It may also be kept secret within the family itself. But the truth sometimes gets out, as in these four cases.

Huma: 'I probably would never have wanted to know'

Media playback is unsupported on your device Media caption Huma: "The shock factor had hit me"

Huma, 32, flicks through her childhood photo album, drifting between pictures of picnics, weddings and family days out at the beach.

"I'd always seen her as my aunt. I think our eyes definitely resembled, we share certain elements and features. But I had no inclination she was my biological mother."

The London-based recruitment consultant was born and raised in Kenya until the age of five months, when she was given away by her father to her aunt, who had struggled to have a child of her own.

Some things are better left unsaid Huma

It was only as a 17-year-old that Huma was told the truth by her biological mother - the woman she had seen as her aunt her entire life - during a birthday party being thrown for her adoptive mum.

"It felt like a script from a movie that she'd rehearsed, it was told in quite a moving way and it left me just taking in the information. It didn't spark any questions for me, I wasn't intrigued, I was just sort of blown away. And then I got on with the rest of the party."

Huma was told not to let on that she knew, because it would tear the family apart. She spent the remainder of her teenage years trying to continue life as normal, despite now knowing her parents were in fact her aunt and uncle. The burden of keeping the secret affected her health, causing to her to lose weight and fall behind at school.

As a child, Huma dreamed of adopting a child when she was grown up, and puts this down to subconsciously always knowing the truth about being given away. She has now worked at rebuilding her relationship with her adoptive mum and dad but does not stay in touch with her biological parents.

"If I had it my way, I probably would never have wanted to know and just live in that bubble," she says. "It would cause a lot less heartache. Some things are better left unsaid."

Kulvinder: 'I found the paperwork and was like, "Wow"'

As a child, Kulvinder (not her real name) would sometimes go to her aunt and uncle's house for a sleepover. During one visit, when she was 10, a cousin let slip that Kulvinder had been adopted - and that there were papers to prove she had been given away.

I can vaguely remember being at home and my biological mother coming and grabbing hold of me and just taking me out Kulvinder

"I didn't know what 'adoption' meant so I actually went through the dictionary and looked it up," she says. "Dad was very particular about his folders, I was careful so he wouldn't find out. Then I found the paperwork and was like, 'Wow, discovering you're adopted at 10.'"

Everyone in Kulvinder's family already knew she had been given away to her uncle and aunt, as they had been unable to have their own children. Kulvinder was the last to find out. She confronted her adoptive parents, though they managed to convince her she was imagining it and the topic was soon forgotten about.

Then, a few years later, her biological parents turned up at her house, demanding her back.

"I can vaguely remember being at home and my biological mother coming and grabbing hold of me and just taking me out. There was a point where they did actually take me off my adoptive parents for a month."

Find out more

Listen to the radio documentary Passing the Baby on Tuesday 4 October at 11:00 and 17:10 BST on BBC Asian Network

When she was 18, Kulvinder's father finally admitted that he was in fact her uncle. But rather than causing a rift, the revelation strengthened their relationship and the pair grew closer together.

Kulvinder now lives in the same town as her biological parents but does not want to have a relationship with them. Instead, she avoids them at the local temple, only saying hello in passing, if they make eye contact.

Surinder Arora: 'Two mums and two dads - I'm so lucky'

Media playback is unsupported on your device Media caption Surinder Arora: "I've been blessed to have love from two mums"

Surinder Arora is one of the UK's most successful Asian businessmen, a multimillionaire with a fleet of luxury hotels to his name. Born in India, the father of three describes himself as being a 'mistake' and was given away to his aunt and uncle within a few days of being born.

As a teen, Surinder fell in with the wrong crowd - he started skipping school and began carrying a knife. On seeing this change in him, Surinder's biological mother decided to take him back, while also relocating the family to London in the hope of a better life.

I got a call from India saying my dad had passed away, while my biological mum here was seriously ill with cancer Surinder Arora

"My other siblings were like, 'We've given him away, why do you want to bring him back into the family?' But my biological mum really wanted me to become a bit more civilised and insisted on single-handedly bringing me over to England."

It was only then, over a casual conversation around the kitchen table, that Surinder was told by his biological parents that he was their son. A young and rebellious Surinder took the news in surprisingly relaxed fashion.

"I was obviously shocked at first but then thought, to have two mums and two dads, I'm the luckiest person in the world."

Surinder attributes his success in later life to the love shown by his two sets of parents, each playing a unique role in his upbringing.

Image caption Surinder Arora as a young pilot

He did, however, have moments where he was torn between his birth parents and adoptive mum and dad.

"I got a call from India saying my dad had passed away, while my biological mum here was seriously ill with cancer. I was torn about what to do but my mum said, 'You're their only son, go to his funeral.' I'm so glad that I did, I'll treasure the love he gave me till my last breath. Then I came back here and shortly afterwards I lost my mum."

Suneil: 'We've known each other as cousins - you're actually my brother'

Suneil (not his real name) only discovered his cousin was his brother when he was in his early 30s. By this point he'd managed to land the job of his dreams, get married and even have children of his own.

One day, while going through emails before a night out with his wife, one message in particular caught his eye. It was labelled "private and confidential".

When we finally met as adults, I suddenly found myself in a room as equals because we were so similar Suneil

"The gist was basically, while we've known each other as cousins our whole life, you're actually my brother and the rest of the family already know. It was literally as out of the blue as that."

At first, Suneil tried to block the email out his mind completely. He began distracting himself with other things but it kept eating away at him and he slowly began piecing things together, from details provided by relatives.

"My understanding is that my biological mum was told to give me away by her father-in-law, as my adoptive parents couldn't conceive. I'm fairly certain the conversation went along the lines of, 'The next ones yours.' It's almost like we're talking about a round of tea."

Suneil had met his cousin several times as a child. After months of talking it over with his wife, he decided he had to see him again - this time as brothers.

"When we finally met as adults, I suddenly found myself in a room as equals because we were so similar. Here was someone I could see myself in. I wasn't angry. I finally I felt I was home."

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