It's hard to imagine a worse start to an adoption reunion. But even highly charged Oprah-style reunions do not always end happily. Some fizzle out; others end abruptly in rows. Some never really take off at all. There is so much emotion invested, so it's little wonder that those involved are often left feeling bewildered and bruised.

"This is the unexpected side of reconnecting that we don't really hear about," says Julia Feast, of the British Association for Adoption and Fostering. "The perception of reunions is often idealistic, but what happens to the relationship in the longer term can be complex."

Most adoption reunions do last, the most recent research shows that 78 per cent are still in touch eight years later (and only around 7 per cent experience outright rejection). "I wouldn't want to put people off looking for birth relatives, as studies show that the vast majority of reunions bring huge benefits; but it's also important not to have rose-coloured spectacles, and I'd certainly like to see more people better prepared," says Feast.

According to Rose Wallace, a specialist in post-adoption, one of the most common problems is that birth parents often have far greater expectations of their reunion than an adopted adult. "While the adopted person often wants to answer questions about their identity, the birth parent has memories of what it felt like to part with the child," she says.

"My birth mother, who I met when I was 30, wanted me to act out the role of long-lost son, but I didn't want a new mother," says Adam, 50. "I just wanted to know where I came from. It was one of the reasons I eventually pulled the plug on the relationship.

"I was excited at the prospect of meeting her. I was struck by the physical resemblance, which I'd never shared with anyone. But she had no more children, and a difficult marriage and wanted more from me than I could give."

Adam believes the relationship was doomed. "[I believe] the initial rejection suffered by an adopted child doesn't go away. I found it niggled away at the relationship."

In any case, he adds, just because someone is a relative, doesn't mean you will like them. "Even in that first meeting, I came away feeling that this wasn't someone I was particularly proud of, which is quite telling," says Adam. "Over time, it became clear that she made a lot of things up. After about 10 years, I'd had enough."

At the other end of the spectrum are reunions that quickly enter the "honeymoon period".

"It can feel a bit like a love affair - but, as with love affairs, the intensity doesn't automatically secure its future," says Feast. "Over time, little things can irritate you and because there's all this history, questions arise. I remember one guy who had a fantastic relationship with his birth mother, but when his own child reached nine months, he got angry. He looked at his son and thought: 'How could you have given me up?' Other issues can arise - the difficulty of divided loyalties with adoptive and birth relatives, for example. The road gets bumpy."

Sue recalls the honeymoon period after the reunion with her birth mother: "I found her the year after I'd met my father and things got very intense. I think it was partly us being two women, and partly to do with my deep need to have a mother and hers to have someone to love her. I remember her putting some money and essentials in a bedside drawer for me, as well as giving me keys to her tiny council flat. To me, this was huge - I felt I had this place to go where I was really wanted. That was attractive and addictive and definitely accelerated the relationship."

But cracks emerged. "I moved on from my initial needs; she didn't. One night it all came to a head when she got seriously drunk on a shared holiday. Things were never the same. When my 30th birthday came and she didn't send a card, I thought, she has done this three times now - once when I was born, once when we didn't have contact for a year after a previous drinking episode, and now this.

"I decided it must end there."

It's not just the people who were adopted who reach breaking point. Philippa made contact with the daughter she had given up as an unmarried teenage mother some 20 years earlier. "After years of feeling she was taking me out of the cupboard and putting me back again at her will, I'd had enough," says Philippa, 60. "The reunion was an eye-opener. Little about her fitted the image I carried of her and I think she was surprised to meet a strong person who had moved on. But she met my other children and it seemed to go well, so I was stunned when, two months later, she said there was no future in the relationship. A year later she contacted me again, then another two years later, and so the pattern went on. I decided to draw the contact to a close.

"It's great that some people reach a manageable relationship without a shared history, but it's also not surprising that others don't. Those involved in a reunion need to be prepared to work out a different way of connecting."

But Philippa, Adam and Sue do not consider their reunions unsuccessful, and are glad they had the experience. This reflects research that shows more than 80 per cent of those who reunite are pleased to have made contact.

"Just to be able to walk down the road and not look at everyone thinking 'Are you my mother or my father?' is enormous," says Sue. "To have had real relationships with real people and to have critical information about my history is even greater. There are rarely situations in life that are wholly positive or negative. Adoption reunions are no different."