Chronic staff shortages in NHS mental health trusts in England and Wales are causing patients to be neglected and exposed to violence on the wards, government inspectors warned yesterday.

The Commission for Health Improvement said mental health remained "the poor relation of the NHS", four years after ministers pledged to make it a priority.

Its inspectors found that "significant national shortages of psychiatrists and nurses are having a major impact on clinical leadership and quality of patient care".

Mental health trusts commonly relied on excessive numbers of agency staff who did not have the skills needed to cope with a violent incident, the commission said. This left permanent staff working long hours and feeling unsafe.

Patients were also concerned about their exposure to violence from other patients. Bed shortages led to inappropriate mixes of patients with different needs. Staff struggled to stop illicit drugs and alcohol.

The mental health charity Rethink said there were good results in areas where extra resources were invested to solve staff shortages. "But services are at best patchy and at worst being shut down because money meant for frontline services is not reaching them," said Paul Farmer, its director of public affairs.

The health minister Rosie Winterton said the government spent an extra £262m last year on improving mental health services. There were 3,655 more nurses and 30% more psychiatrists than in 1997.