When Kisi Assan dropped off her two-year-old daughter at nursery, it was the first time they had been separated since the child’s birth. Following a summons from the Home Office, she then set off to attend a meeting at a nearby immigration reporting centre. Assan [not her real name] had no idea that it was part of a plan to deport her at short notice to west Africa. Shortly after arriving at the centre, the 28-year-old was restrained by eight security officials, and transferred to a detention facility – without her child.

This practice is one of the toxic yet least-publicised elements of Theresa May’s “hostile environment”, introduced when she was home secretary. While Donald Trump’s policy of separating immigrant families has drawn international opprobrium, the practice continues largely unchallenged in the UK. Some say that when the prime minister recently described Trump’s scheme as “deeply disturbing” and “wrong”, she must have hoped her own approach would be overlooked.

Lawyers point out that UK unlawful detention cases are often settled out of court and silenced by confidentiality clauses. Inspired by the universal condemnation of Trump’s separation policy, parents with ongoing cases against the Home Office have spoken out about a system that, lawyers claim, fails to take a child’s welfare into account. “It is cruel and completely unnecessary,” said Janet Farrell of solicitors Bhatt Murphy.

Every year, hundreds of children are separated from a parent who is detained in a UK immigration centre – and numbers continue to rise. According to the charity Bail for Immigration Detainees (Bid), 322 children were separated from 167 parents in the 12 months to the end of July, an increase of 16% on the previous year. A proportion of the children involved will be in the sole care of the detained parent, and have to enter the care system. The Home Office does not keep records of the number of times it separates a child from a parent, a power it wields without apparent oversight.

“There is rarely a more emotive subject than the separation of a child from its parents,” said Celia Clarke, Bid director. “It is shocking that in modern-day Britain our government has the power to do this solely for the supposed purpose of immigration control. In any other setting this would surely cause outrage.”

Assan says she is stunned by the Home Office’s callousness. On her way to the reporting centre on 3 March 2015, the day she was detained, she had called her Home Office caseworker to say the trip was logistically difficult because she had to pick up her daughter. She says the official encouraged her to attend, promising to review the arrangement. On arrival, Assan was told her deportation order had been certified, so there was no appeal. Court documents record that she began screaming and was restrained, with “officers holding her legs, her arms and her head right back”. The Home Office has not disclosed a “use of force” report, despite this being mandatory.

Handcuffed and with her phone confiscated, Assan was taken to detention. At 3pm, when her daughter’s nursery closed, there was no one to collect her: the Home Office had arranged no care. The toddler was taken into emergency foster care. Court documents describe the child as in “acute distress and confusion”.

Speaking through tears, Assan said: “She’s my first child. It was the first nursery session, the first time we had been separated. I had no clue where she was or who she was with.”

Almost two days passed before Assan was told her daughter was in care. It was another month before she saw her again. Case papers chronicle the meeting in Bedfordshire’s Yarl’s Wood centre. “At first, [the girl] appeared uncertain and scared but then she recognised her. It was very confusing for [the child].” In total, mother and daughter were separated for three months. Assan was placed on suicide watch. Her daughter remains traumatised.

“They punished my daughter, an innocent two-year-old. The experience has affected her speech, and she is anxious and scared when I drop her off at school,” said Assan.

Farrell says the government broke its own welfare rules by forcing the toddler into care: the Home Office has until 14 August to respond to the mother’s claim for damages.

Theresa May in 2012 when, as home secretary, she introduced the ‘hostile environment’ immigration strategy. Photograph: Gareth Fuller/PA

Another mother affected by the policy is Leysa Mikel, who was forcibly separated from her two young children for four months. Incarcerated in an immigration centre after a prison term for non-violent offences, the 31-year-old was unable to see her six-month-old daughter and son, aged two.

Attempting to deport Mikel, the Home Office argued she was not the children’s “primary carer” because she did not provide day-to-day care. Yet the reason for this was that she was being held by the Home Office in detention, a ploy Farrell described as “outrageous”.

Attempts to reunite the family were repeatedly blocked by the Home Office, and the two children were in foster care from 3 November 2016 to 1 March 2017.

Court documents outline disquiet over the approach of immigration officials. A letter from social services to the Home Office, dated December 2016, states: “The failure to liaise and take cogent evidence of concern about the best interests of these children into account, even when that concern comes directly from the agency charged with protecting children, is lamentable to say the least.”

The Home Office deadline for responding to Mikel’s claim for damages passed last Thursday, and the family is still waiting. Mikel, who said that her children exhibit acute abandonment fears, added: “The Home Office just focused on getting me deported, regardless of my children, who were born in this country.”

Farrell added: “Why an alternative to detention was not used in this case is bewildering.”

Earlier this month, the Home Office paid £50,000 to a father who was separated from his three-year-old daughter. Known as AJS, he was moved 250 miles away from his daughter to an immigration centre in Dorset, where it was almost impossible for her to visit.

He was released just days before the deadline after which his child could have been placed for adoption.

Visibly upset by the episode, AJS said: “She is my reason for living. I thought I had lost her. I had lost all hope and was about to kill myself.” The Home Office, which was contacted for comment, has yet to apologise in all three cases.

“Why punish a child?” said Assan. “Politicians have kids. They need to start thinking as parents.”