More than 30 years after it was decided that keeping people with learning difficulties in locked wards was medically and ethically wrong, there are still more than 1,600 adults detained in old-style "mental asylums", a report reveals.

There are more than 720 men and women detained in 16 secure hospitals in England, despite a pledge by the Health minister Stephen Ladyman to end this archaic form of treatment by April this year. About 700 more are in hospitals in Scotland and 234 are in Wales. It will be two years before all long-stay hospitals are closed, despite the fact that the move to care in the community started in 1971 and nearly 60,000 people have been resettled.

The report, by Katherine Owen, a researcher from St George's Hospital Medical School, studied women in one hospital before, during and after the move from locked wards into the community. It exposes the regime on long-stay wards where women have scant opportunity to develop as individuals, and have little freedom, privacy or independence.

Ms Owen found that staff obsession with rules and routine led to the "infantilisation" of women, who were either rewarded with treats of sweets, biscuits or cups of tea or threatened with powerful psychiatric drugs. The vulnerability of these patients was highlighted in December in a report by the health service ombudsman, Ann Abraham, into sexual and physical assaults on a 32-year-old woman at Fieldhead Hospital in Wakefield, South Yorkshire. Fieldhead is one of 16 English long-stay hospitals that will miss a government deadline of moving its patients into the community by April.

Mr Ladyman said he was "very disappointed" that the April closure deadline will be missed, despite allocating £20m to make the transition.

The Royal College of Psychiatrists and charities such as the Mental Health Foundation agree that the end of this discredited system is long overdue. But Ms Owen's report also reveals that some of the most vulnerable people in society, who have known nothing but decades of detention, have been badly damaged by poorly handled transfers to the community.

Her report concludes that life did not significantly improve for the majority of the women studied. "Their lives continue to be 'institutionalised'. In only one case did an individual's life improve significantly."