Hundreds of pregnant women without legal status are avoiding seeking NHS antenatal care because of growing fears that they will be reported to the Home Office or face high medical bills, according to charities that work with vulnerable migrant women.

The Guardian has seen letters from one NHS trust sent to women with complex asylum claims warning they will have their antenatal care cancelled if they fail to bring credit cards to pay fees of more than £5,000 for maternity care. These letters contravene NHS guidelines, which state that maternity care should never be denied.

Doctors of the World, which runs clinics for trafficked women, undocumented migrants and asylum seekers whose claims have been rejected, is seeing increasing numbers of women seeking medical help at its clinic in east London in the late stages of pregnancy, who say they are too scared to go to the NHS for fear of high bills or of being reported to the Home Office.

In January, a woman came to the charity’s east London clinic already in labour, having received no antenatal care. “She was very fatigued, she was pale. She had been too frightened to go to hospital because of her immigration status,” said Deman Le Déaut, who runs the women’s and children’s clinic in Bethnal Green.

She was the second woman in four months who had come to the clinic for the first time, at the end of the pregnancy, who had not sought mainstream healthcare. “We are seeing a lot of women six months’ pregnant onwards not accessing medical care. That is incredibly dangerous,” Le Déaut said.

One patient, an asylum seeker from Eritrea, was homeless and living in a bus shelter when she visited the clinic in early pregnancy, having been wrongly turned away from a GP because she had no proof of address.

A number of women have visited the clinic, alarmed by debt-collection letters they have been sent by NHS trusts that instruct them to come to their antenatal appointments with money to make deposit payments of several thousand pounds for maternity care.

“Please ensure you bring your credit/debit card or cash to this meeting. Please note the trust will not accept part payments or any delay in paying the deposit,” one letter sent by Barking, Havering and Redbridge University Hospitals NHS trust states. “Failure to pay a deposit for treatment may result in your future appointments being cancelled. In addition, overseas visitors who incur costs for treatment and do not pay will be reported by the trust to the Home Office and debt collecting agencies. The Home Office will review all records of bad debt and this could be detrimental to any future applications to visit the UK.”

NHS rules stipulate that it is legitimate to ask for payment from those who are not eligible for free care (because they are not ordinarily resident in the UK or because they are living here illegally), but emergency treatment cannot be withheld if a patient cannot pay.

A Department of Health spokesperson said staff should be “especially careful to inform pregnant patients that further maternity healthcare will not be withheld, regardless of their ability to pay … our guidance specifically says that maternity care should never be denied or delayed while a patient’s eligibility is established”.

The Barking, Havering and Redbridge University Hospitals NHS trust said that it had recently “updated” the standard letter to make “it clearer that maternity care would never be withdrawn or appointments cancelled”.

Le Déaut said: “It is bad practice to send these letters demanding credit cards. You are not supposed to threaten pregnant women – documented or undocumented – that you are going to withhold services. We are seeing this kind of letter quite often now. These people have no means whatsoever to pay this debt.”

One patient was telephoned weekly by a debt collection agency, which had a negative effect on her mental health, according to staff at the charity.

The pregnancy discrimination charity Maternity Action runs a helpline for women in this situation and has also noted a rise in demand for its services. “We regularly hear from women who are very distressed about receiving large bills from the NHS for their maternity care. It is pointless sending letters of demand to women who can’t afford to pay for their food and housing,” said its director, Ros Bragg.

The Department of Health spokesperson said no one should be denied urgent treatment and “vulnerable people, including those seeking asylum and refugees, are not charged for NHS care they receive”.

The case of a Nigerian woman who gave birth to quadruplets at London’s Queen Charlotte’s and Chelsea Hospital and incurred a bill of several hundred thousand pounds triggered popular hostility earlier this year, but the charity stressed that its patients had not travelled to the UK in search of free medical treatment.

Sarah Pillai, a volunteer GP who works at the east London clinic, said: “This is not health tourism by any stretch of the imagination. These are people at the outer reaches of society, cleaning, cash in hand jobs, providing the infrastructure for society, but unable to access healthcare.

“The women I’ve seen tend to be very anxious and nervous. A lot of these have been women in hiding until now. Lots of these women present late in pregnancy, which has an adverse effect on their pregnancy because delayed antenatal care can create problems for the mother and baby.”

Staff said there was growing awareness among patients of a controversial memorandum of understanding jointly published by the Home Office and NHS Digital that came into effect on 1 January and set out how the Home Office could request information on immigration offenders from the NHS.

“When they hear if you go to the doctors, the Home Office might be knocking on your door, they choose to stay away,” Le Déaut said. “The results have serious implications; we see women who are nine months’ pregnant coming to our clinic. We assume that some people are giving birth at home”

She said she understood the need to ensure health tourists paid “but a trafficked woman or an undocumented migrant, who has no way of paying bills should be refused care when she is at her most vulnerable?”

Binta, a pharmacist from Sudan, arrived in 2010 to visit her husband, a doctor from Sudan who had a British passport and who had fled Sudan for political reasons. While she was trying to organise permanent residencyshe became pregnant. She was told by the Home Office that she needed to return home to apply for a new visa but did not feel able to travel because she was in the late stages of pregnancy. She was given leave to remain on appeal, but the papers did not come through immediately so she found herself ineligible for NHS treatment.

When the GP referred her for a scan, she was sent a bill for £2,669. “I was very frightened. I thought that they would deport us or that I would be sent to jail,” she said.

Her husband, who has now requalified and is working as an NHS doctor, was unemployed while he studied for UK medical exams and was receiving only £65 a week. “They kept resending the invoice; we received many letters. We couldn’t afford to pay. It distracted me from that beautiful moment of giving birth – all the time I was thinking about the money, are they going to take me to court? It is a part of my life I don’t want to remember again.”

Li arrived in the UK in 2012 after fleeing China because she was being targeted for promoting Christianity. She paid traffickers to get her out of China and arrived in the UK on a false passport. She spent more than a year locked in a house, forced to work for her traffickers, who produced illegal DVDs, to pay back some of her debts. Later she was freed and moved to live with a boyfriend. During her pregnancy, she was wrongly turned away by a GP when she tried to register because she had no papers.

“They asked me to pay £5,000 before I delivered the child. At one of my antenatal appointments, they brought me to a small room and explained I would have to pay more if I needed a caesarean. I felt very scared. There’s no way I can pay that much. I thought about not going to hospital, but I knew I couldn’t deliver a child by myself. I couldn’t cut the umbilical cord.

“When I was in the little room, explaining about the payment plan, I had to fill in a form with my immigration status, my names and address. They said they would hand that to the Home Office. I didn’t know what the Home Office would do – if they could deport me back to China. When I was in labour I was thinking about money all the time.”

She has subsequently begun the process of applying for asylum. She is not working because she is looking after a baby, so is not yet able to begin paying back her debts to the NHS.

We’re interested in hearing from other undocumented migrants or people with a complex asylum situation about their difficulties with accessing NHS care. Please share your stories here.