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.
More top news
Officers are investigating after a piece of tree was dropped from the Birchfield Road overpass onto the A448.
The plans would see Belgrave Gate/Haymarket and Church Gate transformed.
Tributes pour in for Wolves legend and cricket trailblazer Baroness Rachael Heyhoe Flint.