Patients were admitted to hospital wards which were riddled with a debilitating vomiting bug.

Some of the patients moved on to one of the wards then caught the sickness and diarrhoea virus.

Hospitals are supposed to close infected wards to all new arrivals to stop viruses spreading until the area is given the all-clear.

However, hospitals run by Brighton and Sussex University Hospitals NHS Trust were so busy they were forced to use wards where patients and staff had fallen ill.

Details of the incident emerged in an annual report to the trust board drawn up by its infection control team.

It said a total of 300 patients at the Royal Sussex County Hospital in Brighton, Princess Royal Hospital in Haywards Heath and Brighton General Hospital caught the virus between April 2004 and the end of March this year. About 76 staff were also infected.

The report said: "Outbreaks are managed by closing the ward to admissions and transfer and restricting staff and visitors where possible.

"The ward generally remains closed until 48 hours after the last new case and reopens only after a thorough final clean and curtain change.

"Due to bed and admission pressures patients have been admitted to closed wards."

A hospital spokeswoman said the decision to put patients on to a closed ward was only done in exceptional circumstances and at the discretion of a senior medic.

She said the hospital had faced severe pressures at the start of this year in particular, with an influx of elderly patients with severe winter-related illnesses.

The spokeswoman said: "Moving a patient on to a closed ward is not done lightly and was decided only by a senior clinical member of staff."

Most of the infections were believed to be the nororvirus, which is not fatal but can have a debilitating effect on already weak and vulnerable people and slow down their recovery.

Rosemary Shepherd, chairman of the independent patient and public involvement forum for the trust, said: "We were not told about this.

"It is disturbing that if a patient comes in with one thing wrong with them they are put on a ward where they are at a high risk of catching something else.

"It clearly indicates the shortage of capacity at the hospitals and at busy times during winter there is no margin to take increased demand into account."

Mrs Shepherd said she would bring the subject of the infection control report up at the forum's annual meeting on Tuesday.

The report said audits on some of the wards at the Royal Sussex found handwashing facilities were inadequate in some clinical areas, mainly due to the lack of handwash basins.

It also found inadequate storage facilities in many wards, which made cluttered areas difficult to clean.

The spokeswoman said: "The problem we have is that the hospital building is old and that means we have problems with finding space.

"We are working on replacing old building stock."

Brighton Kemptown MP Des Turner said: "It is clearly a matter of concern that infection control guidance has not been followed.

"However, I know how intense the pressure on beds is in the hospital trust and this is not helped by bed-blocking. The situation is not wholly within the hospital trust's control.

Brighton Pavilion MP David Lepper said: "I will also be asking whether there is anything I can do such as lobbying in central government for extra funding and support, which might stop the hospital being forced into such a situation again, whether it is at a busy time of the year or not."