A duty on all teachers, doctors, nurses and social workers to report child cases of female genital mutilation (FGM) to the police will come into force next week.

New legislation announced earlier this year make such disclosures mandatory and professionals who fail to report the illegal practice in under-18s could face the sack.

Under the new law, health and social-care professionals and teachers in England and Wales will be obliged to report all cases of known FGM in under-18s, whether it is disclosed by the victim or seen by the professional.

Failure to report cases within a month, unless there are “exceptional” safeguarding issues, could result in the professionals facing internal disciplinary action or referral to regulators, which could bar them from practice.

At a conference on Monday, Karen Bradley, minister for preventing abuse and exploitation, announced the legal obligation would begin on 31 October.

Bradley told a conference on FGM run by Barnardo’s and the National FGM Centre that despite increased awareness of FGM and increases in police investigations of the crime, “the level at which this abuse is being reported is still dwarfed” compared with estimates of its prevalence in the country.

“This means that too many women and girls are still living in silence and are not getting the protection and support that they need,” she said.

“We need to ensure that where a serious crime has taken place – one which can have long-lasting physical and psychological harm – the police can instigate an appropriate multi-agency response to protect girls and bring perpetrators to justice.”

In Britain, an estimated 137,000 women and girls have undergone or are at risk from FGM, though there is some debate about the exact numbers. The practice can cause infection, problems in childbirth and even death. The practice has been illegal in England and Wales since 1985, but police received only 186 referrals between April 2012 and October 2014. There have been no successful prosecutions in connection with FGM.

Figures published by the Department of Health (DH) last month showed 1,000 newly recorded cases at hospitals between April and June. The figure is expected to rise this month, because of a separate but related duty on GPs and mental health trusts to record any adult woman with FGM for the DH.

Campaigners argue that the recording and reporting requirements are vital in the fight against FGM.

However, this second duty, for GPs, mental health trusts and hospitals to record FGM in any adult woman who goes to see a doctor or nurse for any reason, has caused concern among some medical professionals.

A number of senior clinicians, including three involved in treating FGM survivors, have written a letter to the British Medical Journal warning that a requirement on them to record every female patient with FGM and pass their data to the DH was counter-productive and would hinder strategies to eradicate the practice.

They say the planned data gathering, carried out without the explicit consent of patients, is “ill-considered”, “not fit for purpose” and will bring “already compromised patient confidence close to breaking point”.

The letter acknowledges the government’s work in trying to tackle FGM. The medics stress that they do not object to the Serious Crime Act requirement to report child cases of FGM to the police. But they urge the DH to alter its policy, under a programme known as the “enhanced dataset collection” (EDS), to require them to collect and pass on patient-identifiable data on adult patients with FGM, no matter what they go to the doctor for.

The letter reads: “The Department of Health seems wilfully unaware of the wider ramifications of breaching confidentiality and the impact on the human and healthcare rights of already disadvantaged women and their families. Rather than tackling FGM, this measure is likely to be counterproductive and hinder eradication strategies.”

Brenda Kelly, consultant obstetrician and one of the signatories of the BMJ Letter, said she fears the data could be used to aid a prosecution in the future. Kelly, the director of the Oxford Rose Clinic, which sees 6-10 FGM survivors a month, said the requirement would erode one of the founding principles of the clinic – that it was as a safe space for women to talk.

“Some of these women have taken 25 or 30 years to tell someone what has happened to them” said Kelly. “If you break that safe space and say ‘I’m duty bound to record this information and pass it to the DH, there’s a breach of trust.”

The DH says the data collected will be anonymised and that personal information is needed to avoid duplicate counting. A 53-page document on the enhanced dataset, published by the DH in April, states that the data would support law enforcement, enable further investigations and, as appropriate, prosecutions. It adds: “It should be noted, individual patient identifiable information will not be published in order to achieve this.”

However, Kelly said that this assertion by the DH was inadequate and was not “future-proofed”.

“They say unless there’s a ‘legal gateway in place’ they will not share data with third parties. My fear is if in the next two years, there’s no prosecution, the database will be mined for names.”

Another signatory to the letter, Katrina Erskine, a consultant obstetrician and gynaecologist at Homerton hospital, east London, who has been treating women with FGM for 25 years, said the requirement was a “bad idea”.

Erskine, who spoke out against the failed FGM prosecution in February, said: “The EDS is a ludicrous waste of time and effort and may well dissuade women from reporting their FGM, and professionals from identifying it.”

Commenting on the criticism of the EDS data collection, Bradley said: “This point has been made in relation to so many hidden crimes, like modern-day slaves. We haven’t cracked this without having that [mandatory reporting] and we’ve got to do something to break it. It is underground at the moment. I hope the consequences will not be that women will not come forward.”

Campaigners on FGM said they could not afford to lose momentum on such an important issue of child abuse.

Leyla Hussein, a psychotherapist and FGM campaigner, said: “Its important to explain to the patient what this means. As a pregnant British mother, the scar on my arm was recorded but my genital scars were not. If a mother comes in with FGM and she has a daughter, she has to be recorded. It’s not about going straight to social services, but making sure women get emotional and other support.”

Mary Wandia, FGM programme manager at the human rights organisation Equality Now, said: “Our new official estimates show that 137,000 women and girls in England and Wales are either at risk of – or have undergone – FGM. This is child abuse on a huge scale. We finally have it on the agenda and can’t afford to lose momentum.

“If there are data-protection issues, they should be addressed, but recording and reporting FGM is the only way that we will get a clearer sense of who needs to be supported and protected. Girls cannot afford to wait any longer. This is the time to take strong action to end this extreme violence once and for all and not start complicating the issue.”