The hospital confirmed that it put the security measures in place and disciplined members of staff after the picture was unearthed in February but would give no further details.

However a leaked letter sent to the Chronicle & Echo claimed the picture showed two nurses in uniform and on night duty baring their breasts to the mobile phone camera with patients accidentally caught in the background.

A spokesman for the hospital said yesterday: "We were unable to tell whether the image was added from an NGH computer, but nevertheless the trust blocked access to all social networking sites from its PCs as a result of this incident, in addition to taking disciplinary action against the staff involved."

However, in a new statement issued today, Helen O'Shea, NGH chief executive, said: "We were extremely disappointed on discovering the image, and took steps to have it removed immediately. However we would like to make clear that the nurse involved was not pictured topless.

"The staff involved were disciplined, and we issued a reminder to all staff that we expect them to maintain patient confidentiality and professional standards at all times. I would like to reassure the public that this was an isolated incident and is certainly not typical of the behaviour of our nurses."

The hospital has confirmed the photograph showed the nurse 'dressed inappropriately' but has not explained in what way the picture was inappropriate.

Patient representatives said they were outraged at the breach of confidentiality.

Moya McVicar, the former chair of the hospital's watchdog, said: "To say the least it was not good nursing practice at all to be doing something like that. They should not be getting up to that sort of thing."

The admission came after a Freedom of Information Act request to the hospital asking if it had suffered any breaches of patient confidentiality.

NGH's reply said there had been and said the Facebook posting was an "unauthorised disclosure of one patient image" and called the picture "inappropriate".

It also said that the East Midlands Strategic Health Authority (SHA) was told and the staff involved were disciplined.

Figures obtained through the Freedom of Information Act from 162 PCTs, hospital trusts and NHS authorities showed that there had been 557 incidents of lost data and 794 breaches of confidentiality since January 2007.

Dr Grant Ingrams, of the General Practicioners Committee, a national body, said it was vital NHS trusts cleaned up their information governance procedures ahead of the care records rollout.

He said: "It's not appropriate just to say 'naughty boy' if something happens in a trust, there must be quite draconian action taken against the person who's done it.

"With some of these PCTs if you put all their information governance policies together you've got a book several inches thick, but, if no-one actually knows it, and no-one actually keeps to it, then there's no point."