Hospitals with mental health services are some of the most poorly maintained in the NHS, with a backlog of upgrading work worth nearly £500m, figures show.

Department of Health statistics provided to the Liberal Democrats indicate that, in 2002-3, work worth £493m was needed to bring mental health hospitals up to the DoH's own "acceptable" standards for buildings.

Since 1989, each hospital has judged the standards of its buildings against a five-level scale - the acceptable standard is classed as 'B'. These scores will be fed into the overall star rating for each trust.