The deportation of thousands of British children to Australia, Canada and Southern Rhodesia (now Zimbabwe), created the most catastrophic child abuse legacy in living memory, the national inquiry into child sexual abuse has been told.

The author and social worker Margaret Humphreys, who exposed the scale and suffering of tens of thousands of British children taken from families under the child migrant scheme – a policy that relocated children to areas of the Commonwealth, from the 40s to the 70s – said the physical and sexual abuse, conditions of slavery and terror, removal of identities, and lies that suggested the youngsters’ parents were dead, amounted to a catalogue of crimes against the children.

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“These are human rights violations,” she said. There had been collusion and cover-up by the institutions and agencies, who had kidnapped the children and put them into the hands of paedophiles. In a form of secondary abuse the same institutions who had taken the youngsters away had, in some cases, reacted with hostility when the grown-up children returned to find their families.

The removal of the identity of each child, and the fact that the children were taken so far away from anyone they knew and told they were orphans, aided the abuse, Humphreys said.

The Independent Inquiry into Child Sexual Abuse (IICSA ), in full public hearings, is investigating the sexual abuse of children who were removed from British institutions and families between 1947 and the 70s, and taken to Australia and Canada by various charities and churches, including Barnardos, the Fairbridge Society, and the Sisters of Nazareth.

The children, once abroad, were kept in farm schools, where they suffered brutality and sexual abuse, were used as slave labour and deprived of a proper education.

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“The perpetrators knew there was no one for the children to turn to,” said Humphreys. “No one was going to visit them at weekends, no one was going to send them Christmas cards, and no one was going to celebrate their birthdays. So for the paedophiles this was a group of children where no one asked what was happening to them, and no one cared.”

Humphreys, who set up the Child Migrants Trust in 1987 has done more than any other individual to expose the way British children were taken from families and deported. In the last 25 years she has reunited more than a 1,000 individuals with their families in the UK.

Humphries said deported British children suffered the “greatest betrayal” because they were told their parents were dead when they were not. When she began helping individuals to find their families she started by looking for death certificates.

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“In the early days people would write to me and say, ‘my parents have died, I am an orphan please help me find my family’. I spent a very, very, long time looking for death certificates of parents and of course there were no death certificates because they weren’t dead.”

Telling the children they were orphans, she said, took away all hope that anyone would come and get them, and stopped them asking questions.

Humphreys met one mother who told how she would visit her son every week in a children’s home in Liverpool. “She told me she went to see her child regularly every Saturday in the children’s home, she used to go with sweets. But on this particular Saturday she went and no children were there … someone told her they had gone to Australia.”

She found out they had left just one and a half hours before her arrival. She managed to get to Lime Street railway station as the train carrying the children was pulling away. “She ran on to the platform and saw the children on the train … she was screaming and crying, ‘get the children off, stop the train’. Her boy put his face to the window and shouted, ‘I’ll never forget you mum.’”

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When Humphreys later traced other children who had been deported with the boy, they described seeing a woman running and screaming on the platform as the train pulled away. When the boy arrived in Australia he was told his mother had died in the war. But he knew that was wrong.

It took Humphreys and the Child Migrant trust a month to find the mother after the former child migrant, as an adult, turned to her for help.

“So all of those years, when he was growing up, when he was an adult, when he was getting married, having children, she was there all the time – but missing from his life.”

The IICSA inquiry continues.