The Safe Staffing Alliance (SSA) says wards often have just one registered nurse looking after eight patients.
The SSA says research shows when nurses are asked to look after more than eight patients there is an increased in risk of harm or death.
The warning comes as a poll for the Sunday Mirror and the Nursing Standard journal found that more than three quarters of nurses believe a scandal similar to that in Mid-Staffordshire could happen again.
In the poll of 2,000 nurses, 40% said on their last shift there were not enough staff to provide a safe level of care.
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Outbreaks of rain first thing in the east will ease through the morning, but remaining largely cloudy throughout the rest of the day.
Another cloudy day with outbreaks rain or drizzle and mist in the morning. Some heavier bursts of rain possible at first.
Another cloudy day ahead with outbreaks rain or drizzle and mist in the morning.