The prime minister, Gordon Brown, will apologise today for the UK's role in sending thousands of its children to former colonies where many ended up in institutions or as labourers on farms.
The Child Migrants Programme, which ended 40 years ago, sent poor children to a "better life" in Australia and elsewhere, but many of those sent away said they were physically, emotionally or sexually abused.
The prime minister is due to express the government's regrets over the programme in a Commons' statement.
Under the scheme, which ran from the 1920s to the 1960s, an estimated 150,000 youngsters between three and 14 from less privileged backgrounds were sent to Commonwealth countries such as Australia and Canada, but many ended up being abused in foster homes, state-run orphanages and religious institutions.
Children were often told their parents were dead, while parents were given little information about where their offspring were going.