Media playback is unsupported on your device Media caption Steve Evans report from Berlin on the rise of baby boxes.

Boxes where parents can leave an unwanted baby, common in medieval Europe, have been making a comeback over the last 10 years. Supporters say a heated box, monitored by nurses, is better for babies than abandonment on the street - but the UN says it violates the rights of the child.

It is an unlikely scene for the most painful of dramas. On the edge of a road in a leafy suburb of Berlin, there is a sign pointing through the trees down a path. It says "Babywiege" - Baby Cradle.

At the end of that path, there is a stainless steel hatch with a handle. Pull that hatch open and there are neatly folded blankets for a baby. The warmth is safe and reassuring. There is a letter, too, telling you whom to call if you change your mind.

About twice a year, someone - presumably a woman - treads that path at the secluded rear of Waldfriede Hospital and leaves the baby, perhaps born in secret only a few hours earlier.

Image caption Baby box advocates claim they offer desperate mothers a safe way to abandon unwanted babies

That person - presumably the mother - then turns and walks away, never to see the baby again. The baby grows, but never gets to know who his or her mother was.

The word "presumably" is used because the process is secret and anonymous, so nobody knows who the people are who make that walk, carrying a baby to reverse their steps without one.

So one of the arguments made by those who condemn the system is that it may well be men who are giving the baby away, dumping him or her seems too hard a word. The critics say that baby boxes may be used by unscrupulous fathers or even controllers of prostitutes to put pressure on mothers to dispose of an unwanted baby.

Article 7 of the UN Convention on the Rights of the Child clearly states that every child has 'the right to know and be cared for by his or her parents' - when a child is abandoned, this right is violated University of Nottingham Child Abandonment and its Prevention

The psychologist, Kevin Browne of Nottingham University told the BBC: "Studies in Hungary show that it's not necessarily mothers who place babies in these boxes - that it's relatives, pimps, step-fathers, fathers.

"Therefore, the big question is: are these baby boxes upholding women's rights, and has the mother of that child consented to the baby being placed in the baby box?"

Professor Browne continued: "The baby hatch is so anonymous, and so removed from the availability of counselling, that it creates a damage and a danger to the mother and child."

On this argument, by making it so easy to get rid of a baby, mothers are less likely to get the real help they need in their situation of great emotional trauma and even physical risk.

It is an argument the people who set up baby boxes reject. They say, rather, that they are offering desperate mothers a safe way to get rid of their unwanted babies. Those who don't walk the path to the baby box might instead leave the baby in the biting cold of a public place.

Or worse. A court case has just finished in Germany where a mother was prosecuted for killing her baby by throwing it from a fifth-floor balcony.

Letter stored in the Babywiege Dear Mother of a foundling, We realise that taking the step of giving away your child wasn't easy for you. Please be assured that we will take loving care of your baby to the best of our ability and as such will give him/her a good start in life. Also, the baby should be given a chance to live! Should you change your mind and want your baby back, you can come back to us with full trust. We will gladly help you and are pleased when mother and child are able to be together. Even if you don't, we will still help you with advice. Rest assured that you don't need to worry about the police looking for you. Call us. We are there for you. Remember, one day your child will want to know at the very least the name of his/her mother. If you wish to leave this vital piece of information, we'll be glad to help.

This kind of case is giving a push to the movement for more baby boxes across Central and Eastern Europe, from the Baltic states, down through Germany, Austria, Poland, Hungary, the Czech Republic, to Romania. The law in some countries encourages their spread - in Hungary, for example, it was changed so that leaving a baby in the official baby box was deemed to be a legal act amounting to consent to adoption, while dumping a child anywhere else remains a crime.

Professor Browne thinks that the spread is greatest in countries with a communist past (and so an attitude that the authorities will take over child-rearing) or in Catholic countries where the stigma of unmarried motherhood is stronger.

Baby boxes by country Germany - 99

Poland - 45

Czech Republic - 44

Hungary - 26

Slovakia - 16

Lithuania - 8

Italy - 8 (approx.)

Belgium - 1

Netherlands - 1 (planned)

Switzerland - 1

Vatican - 1

Canada - 1

Malaysia - 1

Also exist in Austria, Japan and the US Source: UN Committee on the Rights of the Child

He did much of the unpublished research on which the UN Committee on the Rights of the Child relied in its assessment of the system. It believes that children have a right to know who their parents are and that right is denied to the foundlings left in baby boxes.

The proponents don't accept that for a moment. Gabriele Stangl, of Waldfriede Hospital in Berlin, said that baby boxes save lives, and so increase rights.

At the box in Berlin, she said, there was safety backed by the full facilities of a maternity unit. Once a baby is in the hatch, an alarm rings and medical staff come, even as the mother walks away unseen. The baby is cared for in the hospital and then fostered before going into the legal system for adoption. In the early period, mothers can return and retrieve their child, but later they can't - adoption is final.

But some mothers do return. One told the BBC how she had been in despair when her child was born. The father was absent, and she was young and in a state of numb shock, so she took the route down the path - and then changed her mind barely a week later.

She followed the advice in the letter she had found in the hatch and returned. She said that, for the first time, she had realised it was her baby. She noticed his hair and eyes, and realised she couldn't give him away. Today, she returns to the unit with pictures of the child she now brings up. The baby box had given her time for her confusion to clear.

It's hard to know the full figures of how many relent - the critics of the system say that in Germany it is well-appointed, with the best facilities, but in some of the poorer countries to the east, baby boxes are less well organised.

But at one baby box in Hamburg, for example, there have been 42 babies left in the last 10 years. Seventeen of those mothers have then contacted the organisers, and 14 have taken back their child.

Steffanie Wolpert, one of the organisers of the system in Hamburg, says it has to be better than providing no facilities at all.

"In 1999, we had five babies abandoned and three of them were found dead.

"So we thought about this situation, and why it happened, and found a new way to help children to stay alive".

But the critics, like the UN Committee on the Rights of the Child, are not convinced. They say that baby boxes are a throwback to the past when the medieval church had what were called "foundling wheels" - round windows through which unwanted babies could be passed.

Maria Herczog, a child psychologist who is on the committee, told the BBC that a better alternative, now as then, was more understanding and help for mothers in difficult circumstances.

"They send out the mistaken message to pregnant women that they are right to continue hiding their pregnancies, giving birth in uncontrolled circumstances and then abandoning their babies".

There is no clear right or wrong in this. It is an argument between well-meaning people. The one voice never heard is that of the mother who walks the path with the baby she bore secretly hours earlier, to return without the bundle. Her tears can barely be imagined.