A quarter of nurses have been discouraged about blowing the whistle on concerns over patient care, a poll has suggested.
The Royal College of Nursing (RCN) survey found that 24% of nurses said they had been warned off raising concerns - in spite of the Stafford Hospital scandal.
RCN leader Dr Peter Carter said many nurses faced a culture of fear and intimidation at work and this was placing patient safety at risk.
The poll, conducted on more than 8,200 nurses, found that 44% would think twice about whistle blowing because of worries about victimisation or reprisals.
One of the key recommendations made by the Mid Staffordshire NHS Foundation Trust public inquiry chairman, Robert Francis QC, was that concerns and complaints should be able to be raised "freely without fear".
But Dr Carter told the RCN's annual Congress in Liverpool: "These responses illustrate that despite the recent attention which has been drawn to the importance of whistle blowing, many nurses are still experiencing a culture of fear and intimidation if they try to speak out. This is putting patient safety at risk.
"One of the key lessons from the Francis report was that frontline staff must feel confident that they can raise concerns about patient safety without fear of reprisals.
"Nursing staff want to provide excellent care, but sometimes the systems they work in do not allow this. Staff know what is safe for their patients and what is not. However, they cannot raise concerns if they feel unsure about what their employer's policy is or what the repercussions will be. In particular, nurses have told us about occasions when they have been bullied, ostracised or belittled when they have tried to raise concerns on behalf of their patients.
"The stakes are simply too high for this to be allowed to continue. Trusts which don't encourage an open culture from the very top will only continue to make mistakes, sometimes with devastating consequences."
A third of nurses questioned said they didn't know whether their organisation had a whistle blowing policy, and of the 64% who had raised concerns, nearly one in ten said they had raised concerns as little as a week ago. Nearly half of the concerns raised were about staffing levels and 21% were about patient safety, said the RCN. Meanwhile, 45% of nurses who had raised concerns said their employer took no action.