I was reviled for 'selling' my baby. Now I'm desperate to find her. It's a living death... she's half mine: Britain's first surrogate mum Kim Cotton reveals the extraordinary lengths she's going to after 40 years

A few years ago, Britain's first commercial surrogate mother, Kim Cotton, joined one of those ancestry DNA sites. It's not a step you'd take if you wanted to keep the past firmly in the past, and yet, she says, she doesn't actively want the baby girl she gave up 40 years ago to come banging on her door. These things are emotionally – as well as legally and ethically – complicated. 'Let's just say, I've made it easy for her to find me, if she wants to,' she explains.

'I'm not sure how I would feel about it if she did, though. I'm not sure, mentally, how I would be, because it would be opening up a Pandora's box when I've tried to keep the lid closed. 'It is 40 years lost, isn't it?'. Kim, a grandmother to seven children (that she knows of) clings to the idea that her biological daughter ('who will always be a baby to me – I can't think of her as a 40-year-old') has had a happy-ever-after life, even though she knows that the opposite could be true.

'It's like a fairy tale. I've written it and this is the story I am sticking to,' she smiles, full of self-awareness. 'I don't want to hear that it is more like a Hansel and Gretel story.'. Indeed, for many the name Kim Cotton is still recalled with a shudder – and Baby Cotton perhaps even more so. A few years ago, Britain's first commercial surrogate mother, Kim Cotton, joined one of those ancestry DNA sites.

All hell broke loose in 1985 when it emerged that Kim – a very ordinary ('and very naive,' she adds) mother of two from Cambridgeshire – was paid £6,500 to have a baby for a Swedish couple, in a deal brokered by a US agency. Kim used her own egg to conceive the child and the sperm of the man, as his wife was infertile. For a time, Baby Cotton was the most famous child in the world. Back then, although it was not illegal, the concept of paying a woman for the use of her eggs and womb was deeply controversial and even scandalous. Emotions ran high, with Kim's position characterised as unnatural and unfeeling – the mother capable of giving her baby away for money.

And the fall-out was brutal, for all concerned. Even as Kim cradled the newborn in hospital, social services were 'interrogating' her, she says. Not long after, the child was taken from her arms in a manner that means even now, 40 years on, she talks about not having 'closure'. I tell her that she seems like a woman who is still carrying trauma, and is perhaps even grieving. She agrees. 'It is a living death. Or maybe a divorce, where you still love someone but you see them with someone else. At the end of the day, she is half mine. She is my daughter. And yet, I set out to do what I did, so I have to live with that.

'I don't want this to come across as if I have had an unhappy life. I really haven't, but for all these years I've sort of put it in a box and closed the lid. I can't torment myself with it. 'I don't know where she is in her life. Hopefully she's a mother by now herself. 'I tell myself that she's had a good life because all the indications were that she would have, and there is comfort in the fact that the judge ruled they would be good parents.'.

And if they were not? 'That would be devastating. Unforgivable on my part. You don't give a puppy to a family without sussing them out, and that's what I did.'. Baby Cotton, whom she remembers had the same blonde hair and blue eyes as her older children Anouska and Jamie, was made a ward of court after being taken from Kim's arms. Only after a High Court hearing was she given to the couple who had paid for her – whom Kim never met and knows little about. They took Baby Cotton on to America, where they lived.

Kim, who sold her story to a newspaper (but only after being outed, she says) was publicly shamed, and privately destroyed. Her mother-in-law didn't speak to her for two years, she tells me today. Her existing daughter would grow up to ask her about the half-sister Kim gave away, 'which cut like a knife because I genuinely never thought of Baby Cotton as a part of my family'. She still has no idea what that Swedish couple thought about the furore – or, to this day, whether they have even told their daughter that Kim carried her.

Kim in 1985 with Baby Cotton who was, for a time, the most famous child in the world. She doesn't really know if the child's original birth certificate – which, by law, had to record her as the mother and her husband Geoff as the father – still exists. Certainly, in the utter mess, no-one ever said 'thank you' for the use of her womb and eggs. 'The agency involved made me the scapegoat, and accused me of breaking the contract, so I'm sure that couple thought of me as a first-class, money-grabbing b***h,' she says.