Disclosures under the Freedom of Information Act reveal several hospitals with just one nurse to care for a ward at night.
The survey, which asked for details of staffing levels on a random night last January, found five hospitals which left whole wards in the care of one registered nurse overnight, in some cases with help from an assistant.
At Watford General Hospital, in Hertfordshire, one nurse was responsible for a 22-bed ward for patients recovering from surgery, and at nearby Hemel Hempstead Hospital, one was left to look after a 22-bedded ward for the elderly.