An inquiry into the issue by the Department of Health reportedly found that about one in five hospital trusts has failed to eliminate them.
Chief nursing officer Christine Beasley, who conducted the inquiry, has identified a number of trusts which need help to separate accommodation and facilities.
"Single sex accommodation is a core commitment in the NHS. It should be the norm in all elective care, when patients are pre-booked in for hospital treatment, and it remains the ideal for when treatment is unscheduled," she said.
Commenting on the report, Liberal Democrat health spokesperson Sandra Gidley said: "Just six months ago we were told that the problem didn't exist - despite increasing numbers of reports from patients suffering this indignity.
"The government have been promising to abolish mixed-sex wards since 1997. Why has it taken ten years for them to publish a strategy to achieve this?"
And shadow health secretary Andrew Lansley expressed anger that his requests for information on mixed-sex wards have been refused while the report on wards has eventually emerged on the day that Tony Blair is expected to announce the date he will step down as leader of the Labour party.
"Labour will never learn that the public are fed up with their style of government - burying bad news instead of dealing with the problems being faced by patients and relatives of patients who simply want to know if the government has fulfilled their promise to eliminate mixed-sex wards in the NHS.
"Despite government pledges on mixed-sex wards in 1997, in 2001, in 2005 and again more recently in 2006 Labour have failed to help and listen to patients and NHS staff."
Health secretary Patricia Hewitt defended the level of care provided by the NHS, saying that it has "an excellent record of treating people with dignity and respect".
"Year after year surveys show that the overwhelming majority of patients feel they have their privacy respected and they receive good care. However this report shows there is clearly still more work for the NHS to do to meet our commitment to eliminate mixed-sex accommodation wherever possible," she added.
"In addition to this report from the chief nursing officer, I have asked the strategic health authorities to publish statements setting out the progress they are making. The NHS chief executive has also put this commitment into the operating framework for the NHS this year."
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