For 10 years, Kate Hilpern has helped adopted people like herself find their birth families. She explains why this intensely emotional journey must now end

It's gone midnight and the phone wakes me with a jolt, although I think I know who it will be. "Was it you that sent the letter?" asks a female voice, tentatively. I sit up and take a deep breath. Every few weeks I post a letter that will change somebody's life. I don't know them and they don't know me, but once they've digested my words, they'll probably smile, cry or gasp and quite possibly, all three.

On this occasion, Elaine, a woman in her late 50s, tells me she's just returned from a holiday to find my envelope on her doormat. But what I really want to know (and can hardly bear the suspense) is whether Elaine is upset, excited or angry by what she's read – that Andrea, the baby she gave up for adoption 40 years ago, wants to meet her.

Andrea had approached the adoption charity Norcap to find her birth mother and this is where I, a Norcap intermediary, come in – making the initial contact and guiding her and Elaine through the powerful emotions that inevitably surface. I know I speak for all 60 of Norcap's trained intermediaries when I say it's a privilege to be involved in these reunions, hundreds of which take place every year – and when things go well, as they did with Elaine and Andrea, I still practically burst with delight. Even when things go wrong, our role is vital in helping people come to terms with difficult news. A birth mother may discover that her child is in prison or an adopted person may find out their birth father has died, for instance.

But a few weeks ago, it was my turn to receive a life-changing letter from Norcap. The charity, the letter explained, will close this month due to lack of funding. The hole this will leave in the world of adoption is mammoth and, for many, unthinkable.

Elaine's story isn't so different from my own birth mother's and thousands of other women in the 1950s, 1960s and 1970s. Both women were teenagers when they became pregnant; both were sent away to a mother-and-baby home; both had little choice but to give their baby up to "respectable" childless married couples waiting in the wings. Incredibly, these women were expected to simply get on with their lives, whereas, in fact, most never stopped thinking about their missing offspring. Meanwhile, many adopted people (and I certainly speak for myself here) longed to know about their roots. No wonder Norcap has mattered so much since it was founded 31 years ago. I've lost count of the times I've heard the phrase "I finally feel complete" following a reunion.

And even when things don't go as hoped, people are nearly always pleased they searched. The adopted person has some questions answered and the birth mother (or father or sibling) gets to know that the person they lost to adoption is OK. And if they're not OK, at least they learn the truth, as one intermediary discovered when she found out that the daughter of the birth mother she was working with had died at just six-months old when her adoptive mum dropped her on her head. "It was devastating for the birth mother," the intermediary says. "But knowing meant she could grieve and I helped her thought that process, including finding the grave and accompanying her there. This was information the local authority kept from her for 46 years."

My own reunion, which I embarked on in 1988 when I was 18, brought me both sadness and joy. My birth mother, I was to learn, regretted her decision to have me adopted and went travelling abroad, where she died 18 months later, aged just 19. My grief hit me hard, although I was lucky enough to meet her family, as well as my birth father and his family. Most of these bonds, particularly with my dad, are strong and almost 25 years later are as entrenched as those within my adoptive family.

As with most of Norcap's volunteers, it was my own experience that led me down the path of intermediary work and my first case could not have been more gratifying. Caroline, who was in her 40s, was insistent that this was not an emotional journey, but simply a "finding out" exercise. Yet Greta, her birth mother, called me within minutes of opening her letter, so excited that she could hardly speak. The two women wrote, exchanged photos and then met and Caroline, to her own amazement, was more emotional and happy than she could have imagined.

In the 10 years since, I've had just about every possible response. One birth mother said it was too traumatic to open up old wounds. One adopted sister called me every month for a year just to tell me how happy she was to have found a sibling. And one elderly birth mother responded to my letter in a blind panic, never having told her subsequent son that he had a half-brother. I calmed and reassured her and she soon softened, even calling me back to ask if she could send photos of herself and ask some questions about her son. Although she felt she could never meet him, she wanted him to know what she looked like and she thanked me for enabling her to spend her twilight years knowing that her first-born had a happy life.

The closure of Norcap doesn't mean the end of intermediary work – adoption agencies also provide a service. But they have nowhere near the number of intermediaries that Norcap has, or do they have the same rigorous training. Few make themselves available 24/7 or have the same level of personal experience and passion about adoption.

For birth relatives, there is an added concern. In 2005 (thanks to Norcap's longstanding campaign in which a landmark case enabled three triplets adopted by separate families to meet) the law was changed to allow birth relatives to initiate contact themselves. As the birth relative is not allowed to know anything about the adopted person unless that person gives consent, the intermediary service becomes a legal requirement. But couple the fact that local authorities are notorious for putting birth relatives at the bottom of their "to do" lists with the reality that local authorities will no longer have Norcap to refer them to, and you can guess the result – birth relatives may wait and wait and many, particularly birth parents, aren't getting any younger.

Also a worry is Norcap's contact register, which enables adopted adults and their birth relatives to register an interest in having contact with each other. Matches are not uncommon and it is unclear at the moment what will even happen to this register.

It would be wrong to suggest that the future of adoption reunions is doomed. Some would even argue that Norcap's time has come. "Like most of its members, Norcap came about by accident," its founder, Pam Hodgkins, says. "Back in 1982, I'd found my own birth family and offered to help a woman who talked about wanting to do the same in a Daily Express article. But the editor published the letter instead of forwarding it to her and I wound up with a sack full of letters. But it was a very different climate – searching was incredibly difficult for adopted people and birth relatives couldn't search at all. Both are no longer true, thanks to our work and the internet."

Others point out that with more recent adoptions becoming increasingly complicated (most children are removed from troubled families rather than relinquished by teen mums), the need for intermediaries will only become greater.

Norcap is entitled to feel a great sense of achievement. In 1982, there was no contact register, there was no right for birth relatives to be the initiators of renewed contact and there was a general attitude that while searching for a birth family may be lawful, it was an unwise and ungrateful thing to do in the likelihood that it would upset birth parents, adoptive parents and probably the adopted person as well. "We changed all those things," Hodgkins says. "We also changed attitudes overall."