The United Nations is increasingly concerned at the spread in Europe of "baby boxes" where infants can be secretly abandoned by parents, warning that the practice "contravenes the right of the child to be known and cared for by his or her parents", the Guardian has learned.

The UN Committee on the Rights of the Child, which reports on how well governments respect and protect children's human rights, is alarmed at the prevalence of the hatches – usually outside a hospital – which allow unwanted newborns to be left in boxes with an alarm or bell to summon a carer.

The committee, a group of 18 international human rights experts based in Geneva, says that while "foundling wheels" and baby hatches had disappeared from Europe in the last century, almost 200 have been installed across the continent in the past decade in nations as diverse as Germany, Austria, Switzerland, Poland, Czech Republic and Latvia. Since 2000, more than 400 children have been abandoned in the hatches, with faith groups and right-wing politicians spearheading the revival in the controversial practice.

Their proponents draw on the language of the pro-life lobby and claim the baby boxes "protect a child's right to life" and have saved "hundreds of newborns". There are differing opinions on this key social issue across Europe. In France and Holland women have the right to remain anonymous to their babies after giving birth, while in the UK it remains a crime to secretly abandon a child.

However UN officials argue that baby hatches violate key parts of the Convention on the Rights of the Child (UNCRC) which says children must be able to identify their parents and even if separated from them the state has a "duty to respect the child's right to maintain personal relations with his or her parent".

In an interview with the Guardian, Maria Herczog, a member of the UNCRC committee, said that the arguments from critics were a throwback to the past. "Just like medieval times in many countries we see people claiming that baby boxes prevent infanticide … there is no evidence for this."

Herczog, a prominent child psychologist from Hungary, says baby boxes should be replaced by better state provision of family planning, counselling for women and support for unplanned pregnancies.

She likened the pro-baby box movements in Europe to the religious right in the US. "Very similar to the United States where we have the spread of the Safe Haven programme with baby boxes in 50 states since 1999. Now we have MEPs arguing for baby boxes and they just reject the convention."

The committee wrote last year to the government in the Czech republic, which has seen 44 baby boxes set up since 2005, asking it "undertake all measures necessary to end the programme as soon as possible".

The ensuing row spilt over borders with two dozen right-wing MEPs, including the current president of Hungary, writing to complain that baby boxes "offer(ed) a solution for women who unfortunately keep their pregnancy a secret and fear to approach official instructions".

In an email to the Guardian, Manfred Weber, German MEP and vice-chairman of the European People's Party – the largest grouping on the centre right – who signed the anti-UNCRC letter, said the issue was one of competing "rights". "Although I am convinced that a child is best raised within an intact family, the safety of children is of higher priority than their desire to know their biological parents," he said.

There is evidence that the baby box idea is popular. A Swiss poll in 2011 found 87% saying baby boxes were "very useful or useful" and more than a quarter of respondents thought every hospital should have one.

Herczog said that the committee is undeterred. "We review countries' adherence to the convention. We did Czech Republic. Austria is coming up. I cannot say for sure but I can imagine we will do the same for Austria (as the Czech Republic)".

Her stance was backed by experts. Kevin Browne of the Centre for Forensic and Family Psychology at The University of Nottingham has just completed a two-year study into the phenomenon. He said of the 27 EU member countries, 11 still have "baby hatches" operating – Austria, Belgium, Czech Republic, Germany, Hungary, Italy, Latvia, Lithuania, Poland, Portugal and Slovakia.

"There is growing evidence that it is frequently men or relatives abandoning the child, raising questions about the mother's whereabouts and whether she has consented to giving up her baby," he said. "You also have to ask whether an anonymous drop allows the authorities to check whether there's a chance for the baby to remain with its family in the care of other relatives."

Browne's research found that the Czech Republic and Lithuania both have an average of seven infants left in baby hatches per year, followed by Poland with six and Hungary and Slovakia with four – and highlighted that baby boxes had flowered in post-Communist eastern Europe.

Politicians in the former Communist bloc dispute this analysis. Miroslav Mikolášik, a Christian Democrat MEP from Slovakia, said that the "communist idea" was "to take away violently a child from a family that they considered as an enemy of regime and place him or her in a state orphanage … If UN convention on the rights of the child's article 8 that guarantees children's right to know their own identity means the death of only one unwanted baby, it is a very wrong article and very wrong convention."

In western Europe the issue is complicated by religious practice and the law. Sari Essayah, Finnish MEP from the centre-right Christian Democrats, pointed out that in Scandinavia "two lesbians can get sperm anonymously and have children. They don't know the name of the donor. So what about the rights of the child? The UN have got it wrong here about baby boxes."

Perhaps the most taxing problem will be Germany, the powerhouse of Europe, which has about 80 baby boxes operating across the nation. The German constitution says all citizens have a right to "know of their origins" and fathers have a right to be part of a child's upbringing. Both are breached when a mother gives birth anonymously. Hatches are tolerated – but earlier this year German ministers floated the possibility of a new "legal framework for confidential births".

In February the German Youth Institute found that the anonymous service had lost trace of a fifth of all abandoned babies – giving ammunition to those who want to end the practice.

However Bernd Posselt, Christian Social Union MEP for Munich who signed the letter to the UNCRC last year, told the Guardian that "our experiences with baby-boxes here in Munich, for example organised by a monastery, have been positive. I know also the problems, but for me it is essential to protect and to safeguard the life of children in extreme situations. All other problems can be solved with good will as long as the child is alive. It is not the decision of an United Nations committee what we are doing to help born or unborn children".