A Healthcare Commission census of all mental health units in England and Wales found 55% of inpatients have to share sleeping accommodation or bathrooms with the opposite sex.

In July last year, Lord Warner, then health minister, told House of Lord peers that 99% of NHS trusts providing mental health services met "single-sex objectives" set out in 2000, requiring all mental health units to provide separate sleeping, toilet and bathing accommodation for men and women.

The 'Count Me In' census, published on Friday, was of 32,000 inpatients in NHS or private sector psychiatric wards on March 31 last year.

Paul Farmer, chief executive of the mental health charity Mind, said: "It is quite staggering how bad the mixed sex wards situation is. The NHS is putting some of the most vulnerable people in some of the most threatening and unpleasant environments."

Clare Allan, an author and former inpatient said: "I've been on about twenty different wards, and only one of them was single sex. Mixed sex wards are notorious for incidents of sexual harassment and abuse. They can feel threatening for already vulnerable patients, and they are often far from being therapeutic environments."