The data, obtained by the Tories, revealed one in seven English trusts used curtains or screens rather than walls to separate men and women.

Many more were unable to ensure patients did not pass members of the other sex when walking to the bathroom. The government said single-sex rooms were a priority for the health service.

A government report in 2007 accepted 15% of trusts still had not achieved it, a point reinforced by a Healthcare Commission survey of 76,000 patients last week.

Under the government's definition of mixed-sex accommodation, patients should be kept in bays divided at the very least by fixed full-height partitions.

The detailed definition was introduced amid much disagreement over what constituted mixed-sex accommodation.