Instances of whistleblowing on poor NHS care are being ignored in almost 50 per cent of cases, a survey of over 3,000 nurses suggests.
The poll for the Royal College of Nursing found nothing was done when fears were raised about issues including patient safety and too few staff being on duty.
More than a third of nurses (34 per cent) said they have been discouraged or told directly not to report their concerns about quality of care.
Some 73 per cent said managers had told them not to speak up, while 24 per cent said work colleagues had said it was a bad idea.
The RCN said the results suggest pressure on staff is intensifying - in 2009, just 21 per cent of nurses said they had been discouraged or told not to speak out.
The survey follows heavy criticism of nursing care in a series of reports from the Care Quality Commission and the Patients Association.
It found that more than 80 per cent of nurses had raised concerns with employers about issues relating to NHS wards.
Yet 84 per cent admitted they worried about being victimised or expected a negative effect on their career from whistleblowing.
Of those who reported concerns, 38 per cent had filled in incident forms (an official record regarding threat to patient safety), while 72 per cent had told their line manager.
Overall, just 20 per cent of nurses said their employer took immediate action, down from 29 per cent in the 2009 survey, while 48 per cent said no action was ever taken.
This compared with 35 per cent previously.
There has been an improvement in knowledge about whistleblowing, however, with 73 per cent of nurses aware their trust has a whistleblowing policy. Two years ago 45 per cent did not know either way.
But only 49 per cent of nurses surveyed knew they could report their concerns to other organisations such as the CQC.
And only 42 per cent were aware they were protected in law from reprisals if they raised concerns about wrongdoing.
RCN chief executive of the Dr Peter Carter said: “It is extremely worrying that nurses are being explicitly told not to raise concerns - after all we have learnt about the consequences when problems are not tackled.
“Cases such as the terrible situation that arose at Stafford hospital, precipitating a major public inquiry, should be adequate warning about the consequences of slashing staffing levels and ignoring staff concerns.
“It’s very important that, when we know 56,000 posts are at risk in the NHS, staffing levels across the board don’t lead to another disaster.”
Dr Carter said senior managers “must demonstrate in practice” that concerns are welcomed and will be acted upon.
He said staffing was an issue.
“It is patients who suffer where staffing levels are eroded and concerns are not dealt with, so the impact of cuts cannot be underestimated.”
Public health minister Anne Milton said: “Nurses have a professional duty to express concerns about patient care and anything that goes against that is simply unacceptable. “We are enshrining whistleblowers rights in the NHS Constitution.”