Many hospital patients do not speak out about poor care as they think it will lead to even worse treatment or not make a difference, a survey suggests.
Staff said they would like more patient feedback
Consumer group Which? polled 1,000 NHS patients and found 49% unhappy about an aspect of their stay, such as food, cleanliness or organisation of care.
But fewer than half complained, despite a separate survey showing staff would welcome more feedback.
Complaints systems need to be open and accessible to all, regulators said.
Which? said a culture shift was needed in the NHS to encourage patients to give feedback and make sure their views were heard.
Of the patients who had not complained about their care, even though they had been unhappy, more than a third thought raising an issue would not make a difference.
A quarter said they just "expected their stay to be like that".
More than one in 10 thought complaining could compromise the care they received.
Even among those who complained, most felt standards would not improve.
In a survey of 250 members of hospital staff, 99% said they would like to hear about their patients' concerns and most said they thought gathering feedback would drive improvements.
Two-thirds felt patients did not give enough feedback.
However, patients do not always have the chance to make their views heard, the survey results suggest, as only 17% of patients were actually asked for their views.
Nick Stace, director of campaigns at Which?, said there had been a lot of talk from politicians recently about patient-centred care but this was "more rhetoric than reality".
"We've identified a deadlock in the system that's led to a real complacency culture existing in the NHS and a service that doesn't tackle the issues that matter to patients."
Prime Minister Gordon Brown said the NHS had improved a lot over the last 10 years but there was still much to change.
He said that was why "the voice of patients and a higher standard of personal care" was at the centre of the government's vision.
A spokesperson for the Healthcare Commission said people wanted their complaints to be handled quickly, robustly, independently and at a local level.
"It is important that trusts make their complaints systems open and accessible to all.
"That means creating an environment that provides reassurance that patients complaints will be listened and acted on."
Katherine Murphy, of the Patients Association, said patients found it very difficult to complain and very few actually said anything while they were in hospital as they felt very vulnerable.
"We need to make it much easier for patients to complain and reassure them that it's not going to jeopardise their on-going care and something constructive will come out of it."