Patient care is being neglected at least once a week due to a shortage of available nurses, according to four out of 10 members of the Royal College of Nursing (RCN).
In its annual survey of nurses, the RCN found that 55% of its members said they were unable to provide the care they wanted because they were so busy, and there were not enough staff to meet needs.
Almost two-thirds said their workload was too heavy, putting them under too much pressure.
The survey also found that 200,000 nurses expected to retire in the next 10 years, and with fewer being trained, the current number may soon fall even lower.
A series of demands will be made by the RCN ahead of the general election, including giving nurses time to train, regulating the drinks industry and improving long term care.
Dr Peter Carter, head of the RCN, said: "Staff are concerned that they are delivering the basics but are unable to provide the full range of quality care they would like."
A Department of Health spokesman said: "The local NHS must ensure it has the appropriate number of staff to deliver services for patients. It is important that it helps staff to use innovation and new technology to drive up the quality of care and deliver value for money."