The Home Office has offered a formal apology and will pay compensation to a pregnant asylum seeker who was unlawfully arrested and detained at Yarl’s Wood immigration removal centre.

The government admitted the woman, a Congolese asylum seeker who was arrested in 2014 when she was five months pregnant, should not have been detained and has announced that it will review its existing policy on the detention of pregnant asylum seekers.

Under current guidelines, pregnant women are treated as vulnerable people who are unsuitable for detention and should only be detained “exceptionally”. But according to a report by Her Majesty’s Inspectorate of Prisons, there were 99 expectant mothers detained in Yarl’s Wood in 2014 and only nine were removed from the UK. Details of the current number of pregnant asylum seekers in detention have not been released by the government.

The solicitor acting on behalf of the woman, Jane Ryan at Bhatt Murphy, hailed the settlement as “groundbreaking”. “This is a great victory and a strong basis on which to argue that the detention of pregnant women should be ended altogether. The Home Office has been repeatedly criticised about its practice of detaining pregnant women. The apology and agreement to review both the policy and practice is an extremely important recognition that the system must change.”

In the apology, the Home Office accepted that it had breached its own policy. The apology, from an unnamed assistant director of the Home Office legal team, states: “I apologise on behalf of the Home Office for unlawfully detaining you while you were pregnant.”

The woman, who was subjected to no notice arrest in Cardiff on 3 February 2014, was held for 10 hours at Cardiff Bay police station and then transported to Yarl’s Wood in an eight-hour journey. She was due to have her 20-week scan but was not given this check during the month she was held in detention and was seen by a midwife just once.

The Guardian interviewed the woman while she was detained in Yarl’s Wood. She was in a distressed state and said she had been denied antenatal care. “I am very worried about what is happening to my baby,” she said. “I feel like I am being treated like a criminal here although I have not committed any crime.”

In the settlement, the Home Office accepts that the woman was unlawfully detained in breach of the government’s published policy and that antenatal care “did not meet the standards expected”, especially in the failure to provide the 20-week scan.

Human rights campaigners and health professionals, including the Royal College of Midwives, who have repeatedly raised concerns about the detention of pregnant women at Yarl’s Wood, welcomed the settlement. The Medical Justice charity, which has documented the problems experienced by pregnant women in detention, described the settlement as “momentous”.

“Despite our medical evidence and damning reports by HM Inspector of Prisons and the Independent Monitoring Board, the lobbying of the Royal College of Midwives, and shameful depictions of Yarl’s Wood guards’ treatment of pregnant detainees caught on Channel 4 News undercover cameras, the Home Office have repeatedly failed to admit the harm inflicted on pregnant detainees,” said Emma Ginn, coordinator of Medical Justice.

The charity’s dossier, Expecting Change, exposed the harm done to pregnant women in immigration detention, including at Yarl’s Wood.

Louise Silverton, director for midwifery at the Royal College of Midwives, said: “The Royal College of Midwives has for some time now been calling on the Home Office to end the detention of pregnant women at Yarl’s Wood. Home Office guidance states that pregnant women should only be detained in exceptional circumstances and this guidance is still not being adhered to. The centre was home to 99 pregnant women in 2014 and this is completely unacceptable.

“Some pregnant women have reported receiving inadequate healthcare, which clearly puts their unborn baby at risk as well. The women detained at Yarl’s Wood have a right to be cared for in a dignified and respectful way, just like any other pregnant woman. Yarl’s Wood and other immigration removal centres are unsafe for many vulnerable detainees including pregnant women. Pregnant women are only supposed to be detained if their removal is imminent and at Yarl’s Wood this is not the case, which is most concerning.”