Last week the troubled pop star Britney Spears lost custody of her two children. Whatever your view of Spears’s agonisingly public unravelling – appearing with no underwear, shaving her head, driving without a licence, driving with a child on her lap, charged with a hit and run accident – last Monday’s judgment awarding custody of Sean Preston, 2, and Jayden James, 1, to her bitter exhusband Kevin Federline highlights a growing trend.

Until a few decades ago few would have expected a mum to lose custody of her kids when a marriage broke down unless she was an alcoholic, a junkie or had walked out of the family home to pursue an affair. Which doesn’t mean that the heartbreak and social stigma back then were any the less.

The broadcaster Anne Robinson, whose 27-year marriage to her second husband John Penrose ended last week, has movingly described her reaction to the court proceedings 30-odd years ago that ended with her first husband, Charlie Wilson, becoming the main carer of their then three-year-old daughter. “I was so ashamed of losing Emma I was stoic, and keeping it a secret was pretty bad. I lived with a dull ache.”

But these days, even though it’s still seen as a massive maternal failure if a mum loses her children, with one in three marriages breaking up and 70% of women going out to work it’s happening more and more. Judges in the family courts, which last year heard 400,000 cases, are increasingly making shared residence orders, which split children’s time between both, often working, parents, as well as orders giving custody to the father.

A precise picture is hard to come by: the family courts, which have been heavily criticised for being both secretive and unjust, admitted last week that the only data they had were five years out of date. Those figures show that in one month in 2002, in four out of 10 cases mothers were not awarded sole custody. Since then the figure has almost certainly increased.

Many such mothers are not “unfit”. Often they are excellent mothers, middle-class professionals who had no idea that pursuing a career was putting them at such terrible risk.

“It’s the great taboo subject,” says Ros Edwards, professor at London South Bank University. “If you don’t have your children living with you then you have ‘failed’ and you are not being a proper mum in some way. I feel for these mums. They feel they are being judged and found wanting.”

Carole Walton, a police officer from North-amptonshire, is one of thousands of mothers in Britain whose children no longer live with them. This weekend she will be making the 300-mile round trip she makes every second Friday to pick up her two children, now aged seven and nine, for a precious weekend together. She also sees them for eight weeks holiday a year.

“They are cracking kids,” she says proudly. “They cope so well. I pick them up and they will jump in the car and say, ‘Hi Mum’. This summer we went to Disneyland – four whole weeks of being normal.”

When the children were born, she and her then husband agreed that as the higher earner she would go back to work full time. So, when they were three months old, she resumed her 7am-3pm working day, returning home to take over from her husband as he shuttled out the door to start his five-hour shift. To her horror, the courts decided that since her husband looked after them during the day he should be the main carer after the divorce.

“I look back now and the thing I would say to any woman who considers doing the equality role swap – leaving your husband in the home – is, ‘Don’t do it. Never do it. You will be punished’. I did it for the right reasons but it came back and bit me.”

Walton, who has since married a fellow police officer, says she is “desperate to get my children back” and haunted by fears that her children will, as they grow older, be reluctant to leave weekend activities such as local football matches to see her.

“The worst thing is that you are in a constant state of limbo,” she says, her voice faltering slightly. “The hurt never goes away; it never gets any better. You learn coping strategies to get by. For me it is accepting that, at the moment, I can’t change anything. I have to make the best of it when they are with me, try to give them a good, stable life. I keep busy; then I can cope.”

Walton is far from alone. In researching this article I was unprepared for the tide of maternal misery I encountered. Last week mothers trying to tell me their stories broke down sobbing as they recalled details of how they used to plait their child’s hair before school or cuddle up with them in bed at night. One talked of suicide and having nothing left to live for. The saddest of all the stories were from mothers whose children were now adults yet hadn’t, as many in this situation hope, renewed their relationship once they were grown up.

Penny Cross, chairwoman of Match, a charity for mothers living apart from their children, often following acrimonious divorces, hasn’t seen her children for years. After her marriage broke down, she says, they turned against her. When her eldest son died nine years ago she couldn’t attend his funeral. Now, even though the youngest is in his twenties, they want nothing to do with Cross, a softly spoken professional woman who spent thousands of pounds in the courts fighting to maintain access to her family.

“There is a terrible stigma attached to this,” says Cross. “Even in the 21st century, when women have far more equality with men, they are still perceived by society to be very, very bad women if they are not living with their children. I do not think my children will come back ever . . . There is a secret sorrow, a bereavement cycle you go through.”

The double standard applied to mothers and fathers, which has been identified by researchers such as Sandra Kielty at the University of East Anglia, makes the sorrow of these mums even harder to bear. While you can be a “good” divorced dad by seeing your kids occasionally and providing financially for them, a mum in a similar position is viewed as unnatural. Cross confirms that many of the charity’s members pretend they don’t have children. “They keep their status as mothers apart from their children a secret,” she says. One mother told me she felt like a “leper” in the playground once the other mums knew her children stayed with her only occasionally.

Some fathers given custody by the family courts are even being accused of behaving as embittered mothers have done, using the power of a residence order to limit contact between the children and their former wife. Alison Smith (not her real name) last saw her children several years ago, even though she has a shared residence order which she spent years and £70,000 battling through the courts to obtain. She says the children have been turned against her. “They say they don’t love me, that I’m not their mum.”

She still goes to school meetings and talks to teachers about her children’s progress, and sends them birthday cards and text messages via her exhusband. It’s the only way she can try to keep in touch. “When your whole raison d’être is taken away, you reach rock bottom and try to find a way of taking one day at a time,” she says.

She, too, thinks the fact that she was a working professional woman was held against her when it came to deciding custody. “If I had been a stay-at-home mum I would not be in this situation.”

Britney may find in this, her latest trial, more support than she expected.

Read the alphamummy blog

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?