Rebecca Bunting is excited about the weekend. She's flying from London to Tallinn, the capital of Estonia, where a little boy will be waiting to greet her at the airport.
'It's his fourth birthday,' she says, smiling. 'I haven't seen him for three months and I can't wait to see how much he's grown, how much he's learnt.'
From the way she's talking you'd imagine Rebecca is going to visit a nephew or a friend's child. Instead, this tall, attractive 28-year-old from London is going to spend a long weekend with her son, a son whom she left two years ago when she walked away from him and her husband, and with whom she has no plans to live permanently again.
'He has a very good father and grandmother. I feel he's better off living with them than with me,' she says calmly. 'If my instinct was otherwise he'd be with me, but I just can't be sure that that would work.'
Drinking green tea in the bar of a London hotel, Rebecca comes across as a confident and focused young woman. An English teacher, she now lives in Brighton and when we meet she's just been shopping for a dress to wear on a theatre outing.
Yet public perception of women like Rebecca, who have chosen to live away from their children, is that they are at some level inadequate. In a society where maternal love is revered, anyone who fails to put their children before herself is seen as unnatural. Whispers follow: 'What's wrong with her? I could never do that.'
Sarah Hart is the co-chairwoman of Match, a charity for mothers who don't live with their children, and author of A Mother Apart, a book for the 200,000 or so British women estimated to be in this situation. She says that there is still a huge discrepancy in how we view mothers not living with their children, as opposed to fathers.
'With men we acknowledge it's very painful for them to be separated from their kids but that this is just how things work out. But when a woman does it our judgment is unforgiving,' she says. 'The assumption is that she must have done something wrong, that in some way she must be unfit.'
Fiction is full of admonitory stories about women who break this taboo. Anna Karenina leaves her husband and son to run off with another man, only to end up committing suicide. The 1970s hit film Kramer vs Kramer told of a middle-class woman, played by Meryl Streep, abandoning her young son to 'find herself' and discovering on her return that the child no longer wants her.
Tony Parsons told a similar story in his bestselling novel Man and Boy, based on his experience of his wife, the writer Julie Burchill, leaving him and their five-year-old son, Bobby. Burchill described public attacks on her as 'a load of pompous cant, basically. Men do it all the time.' None the less, 30 years later she and Bobby are still estranged.
Equally vilified was Frances Shand Kydd who in the late 1960s left her husband, Earl Spencer, and four children for another man. Her young daughter, the future Diana, Princess of Wales, always made it clear she had been forever scarred by the abandonment.
History largely chose to ignore the fact that Shand Kydd had in fact fought and lost a vicious custody battle, an anomaly at a time when courts virtually always awarded custody to mothers. But the Children Act of 1989 stipulated that justice must be 'gender neutral' and not assume the mother was always the primary carer.
This, combined with increasing numbers of women becoming breadwinners and more and more men 'house husbands', has led to a sudden, steep rise in women living away from their children. Today the Child Support Agency has 55,000 women on its list of absentee parents required to pay maintenance, about five per cent of its caseload.
Although no legal arrangement is in place, Rebecca Bunting sends money monthly to support her son. She was just 23 and a drama student in London when she became accidentally pregnant.
'I'd never dreamed about marriage or children but I surprised myself and my friends by feeling really positive about it,' she says. Her boyfriend found work in his home town of Tallinn so, seven months pregnant, she moved there and married him.
Almost immediately, however, their relationship disintegrated. 'Very quickly we lost any fibre of the love we'd once had for each other.' Rebecca wanted to return to London but was too pregnant to fly. She ended up giving birth by caesarean section in a hospital where none of the staff spoke English.
'My husband was working away from home, I was living with my mother-in-law, a London girl in a small town no one had heard of, where it was always cold and dark. I thought, "How has this become my life?"' She crosses her arms as if cradling a baby. 'No one spoke my language and I was with this child I had to feed and care for, 24 hours a day, for ever. It was hard to feel much joy.'
In such alien surroundings Rebecca found it impossible to fall in love with her baby. 'I found the routine of being a mother deeply unfulfilling. With the bond other mothers seem to have it might have been bearable, but I just couldn't feel it in me. My son was part of me, I grew him, I breastfed him for a year, but that connection just wasn't there and that was so difficult to live with.'
Only on occasional trips to London did Rebecca 'feel the fog lifting'. So when her son was two she decided to return for a long stay while he remained with his father and grandmother.
'Initially, we agreed it would just be for the summer but I think I knew I might not return,' she says. This suspicion was quickly confirmed. 'As soon as I got home I just felt so full of life. I felt something had returned, and it was me.'
It sounds as if Rebecca had a severe case of postnatal depression. She nods. 'If I'd been in England that might have been addressed and I might have thought, "Is there something I can do about not bonding with my baby?" But in the circumstances my remedy was just to leave.'
She shrugs. 'I had a bad time but women give birth in terrible places – in Iraq – and they cope and form a bond with their children. Even back in England, where I felt so much happier, I wasn't sure that I would feel 100 per cent with my son there. I just couldn't guarantee stability.'
Despite her resolute air now, for a long while Rebecca was torn with self-doubt. 'I thought, "What the hell is happening? I had a child and I've left. People don't do this. I must be a terrible person." I wouldn't say I was in turmoil but I couldn't quite balance myself. I had to sit down and say, "This is who I am." In the end I had to think what was more damaging: me leaving or my son being with a mother who wasn't a happy version of herself.' She adds that her own mother was not particularly maternal. 'Perhaps if she had been, things would be different, but as it is I know what it is to live with a mother who doesn't take to it naturally and it's not very nice.'
Two years on Rebecca talks to her son regularly and aims to see him every three months. 'It's lovely now; I enjoy him and learning about him. I see having him as a wonderful thing in my life and I'm looking forward to the future of it.' Are maternal feelings beginning to develop? 'We have a unique mother and son relationship,' she says firmly, avoiding the question.
Sarah Hart stresses that women like Rebecca who actively chose to leave their children are the exception rather than the rule. Three quarters of the women she counsels may have walked out, but they intended their absence only to be temporary.
'They are suffering terrible stress at home and leave in a hurry, thinking they will come back soon to fetch the children and then they find out with horror that this is not so easy.'
Angela Harper, 50, who lives near Glasgow, walked out on her three sons, then 15, 13 and nine, 10 years ago, after 16 years in an unhappy marriage.
'I stayed all that time for the children's sake, but in the end I couldn't do it anymore,' she says. 'I ran away thinking that this would jolt my husband into seeing how miserable I was and we could sit and talk, but then everything spiralled out of control.'
Instead, her husband applied for sole custody of the children. Largely because Angela had left the family home, he won. 'I was an absolute mess but I never, ever expected to lose my children. I was in unbearable pain.'
Because she had left, few sympathised with her. 'People who'd known me before understood the kids were my life. But people I met later were so harsh. Once they found out I'd left my kids they didn't call me back, they never went out for coffee with me again, they said, "Over my dead body would I leave my children." They assumed it must be crime, drink or drugs related; they didn't realise life was so bad. My doctor saw what a state I was in but he just said, "You should have thought of that before you left." It was such a lonely place to be.'
Sarah Hart says that, stripped of their main role as mother, many of her clients are suicidal. 'Their entire previous identity suddenly vanishes. They're asking themselves, "If I'm not a mother, then who am I? How can I carry on living?"'
Sally Smyth, 35, from Croydon, Surrey, has not lived with her three children, aged eight, six and five, for two years. In desperation, she sent them to live for what she thought would just be a couple of months with her ex-husband when she found herself under intolerable pressure as a single mother. Now, however, he has custody and she can only visit occasionally.
'I have to avoid public transport because the sight of mothers and their children makes me feel sick,' she says, near to tears. 'If something to do with children comes on television I have to leave the house. It doesn't get better. You think you're coping and then you visit the children and it just hits you. In some ways it would be easier if I just never saw them again, but of course I couldn't do that because it would be so devastating for them.'
However understandable their motives, all the women I spoke to were tortured with guilt about the effect their actions would have on their children. Even Rebecca, who is adamant she made the right decision, has found it impossible to resume her former, carefree existence.
'There was no way I could just revert to the lifestyle of a 23-year-old. I had a sense that since I had done this thing I needed to do something with my life, to set a good example, to justify living apart from my child.'
Among other things, she is now involved with the Green Party and volunteers as a speech and language therapist.
'I felt so trapped before, and now I really value being able to choose. I've regained my freedom but I want to contribute it to bigger causes.'
She is adamant she will never have another child, both out of respect to the son she already has and because she is convinced she was not meant to be a mother. Meanwhile, her friends are starting to settle down.
'Some of them can't wait to have babies. Great, good for them.' She pauses. 'There's a hype about getting married and having a baby, but it wasn't for me. I want to do what I want to do and my life is going to be about other things.'
Some names in this article have been changed
Julia Llewellyn Smith