Home Office workers embedded in local councils are sitting in on interviews with destitute migrant families and gathering personal information on subjects ranging from health conditions to how their child was conceived, the Guardian has learned.

In documents made public after freedom of information requests by the migrants’ rights charity Project 17, 10 London boroughs revealed that they had employed on-site immigration officers.

Haringey council did not renew its contract with the Home Office in 2017 after a string of complaints against the embedded worker. Lewisham council said it had recently decided its embedded officer should no longer have direct contact with families.

The revelations drew condemnation from human rights lawyers, charities and politicians, who described the practice as “totally unacceptable” and “a gross perversion of the purpose of the law”.

The news will add to wider concerns about the Home Office’s role in local authority work. Last year the Guardian revealed that homelessness charities and local authorities were passing on information about foreign rough sleepers to the Home Office, leading to their removal from the UK.

Section 17 of the Children’s Act places a duty on local authorities to provide financial support and accommodation to ensure a child’s wellbeing and prevent them from becoming homeless. Councils interview families in child poverty assessments to determine their eligibility for this support.

In some London boroughs, uniformed Home Office workers are now present in assessments where sensitive personal information is sometimes divulged, including health conditions, how a child was conceived and engagement in sex work.

Lawyers and charities have expressed concern that the presence of a uniformed Home Office worker in interviews is invasive and risks deterring destitute families from accessing support.

“Local authorities have a clear obligation to safeguard the welfare of children. That support is a right, and we are concerned that families are afraid to access that right because of data-sharing with the Home Office,” said Jennifer Ang, a human rights lawyer at JustRight Scotland.

A memorandum of understanding released under FoI laws sets out the terms of employment for immigration officers to “conduct real-time immigration status checks” on families applying for support.

Hackney, Haringey, Southwark, Greenwich, Enfield, Barking and Dagenham, Lewisham, Harrow, Croydon and Bexley have all employed officers.

A Home Office spokesperson said officers assisted councils with supporting destitute families and sat in on interviews “when specifically asked to by the local authority”.

Councils told the Guardian the Home Office workers helped to resolve families’ immigration status and ensure they were supported appropriately.

Many people claiming section 17 support have no recourse to public funds and are ineligible for housing and employment benefits as well as most NHS care.

The Labour MP Jess Phillips said: “There is no way a vulnerable woman who comes to a council should have their immigration status have anything to do with their case for safety for them and their children – that is totally unacceptable.”

Councils are legally required to inform the Home Office if an applicant for support is unlawfully resident. Jennifer Blair, barrister at No5 Chambers, said there was “no legitimate basis” for Home Office workers to be involved in interviews before the council had established people may be in the country illegally.

Councils have taken a variety of approaches to including on-site immigration officers in the assessment process. Harrow said an officer would only interview families who had unresolved immigration issues. Bexley council said its Home Office worker was involved in all initial interviews with people claiming section 17 support.

A spokesperson for Bexley council said the officer “ensures that persons who are unlawfully present in the UK cannot obtain support or services for which they are not entitled”.

Blair said immigration officers did not need to interview families to carry out immigration status checks that could generally be completed using Home Office databases. “It really feels like the purpose of having somebody at the interview is to intimidate them and to try and get removal action taken against them as quickly as possible,” she said.

Some applicants have signed consent forms that allow their personal data to be shared with the Home Office. But there are concerns that these forms could sometimes be signed under duress.

Ang said a consent form could give additional data-sharing powers. “But if someone says ‘I came in and I had to sign it to access support’, that consent might not be valid,” she said.

Bethan Lant, head of casework at Praxis, said social workers who requested Home Office support in these assessments regularly threatened to separate families.

In a recording heard by the Guardian, a social worker tells an applicant with leave to remain that the Home Office worker present at the interview could deport her, in front of her daughter. “The impression being given by officers is that if you need help you have to consider going back home, which is absolutely not the case,” Lant said.

One Nigerian claimant told the Guardian that an immigration officer criticised her for sending her children to live with a family member while she was depressed. “They said: ‘Why would you abandon your kids? What kind of mother would do that?’ They made me feel like a criminal.”

Campaigners say the practice of embedding immigration officers in local councils is harming vulnerable children. Chai Patel, legal policy director at the Joint Council for the Welfare of Immigrants, said: “Section 17 support is designed to ensure that children and their families are not left destitute, homeless or starving. For the Home Office to use it to gather personal data on those families for immigration enforcement purposes is a gross perversion of the purpose of the law.”

Amy Murtagh, the interim director of Project 17, said: “Our research has shown that the perceived threat of possible detention or deportation deters families from accessing support. As a result children are being left homeless, in situations of dire poverty or at risk of exploitation.”

A Home Office spokesperson said: “Immigration officials are based in local authorities to provide details of individuals immigration status to help ensure those that need support receive it. This includes helping single mothers, families with young children and individuals who would otherwise be destitute.”