NHS hospitals are failing to listen to concerns raised by visitors, contractors and others, a Freedom of Information (FOI) request by Healthwatch England has found.
The figures released revealed 1 in 3 hospitals did not record complaints made by third parties in hospitals, 46 out of the 123 trusts who responded.
Present complaints regulations allow anybody to complain, however some trusts said that they would only investigate such complaints if the patient gave their consent.
Others trusts record the incidents as general feedback which are not recorded in official complaints figures reported to the Health and Social Care Information Centre.
Of those who responded to the FOI request 30 trusts investigate such incidents and had details of how many cases they had had in the last three years.
From 2011 to 2014 8,448 such complaints were made, 18% of the overall 46,753 complaints made about NHS trusts.
Research earlier this year showed that almost two thirds of those who witness or experience poor care do not report it.
Anna Bradley, chair of Healthwatch England said: "Hospital patients often feel incredibly vulnerable and too scared to complain when they receive poor care. And yet widespread misapplication of the rules is preventing concerned citizens standing up on their behalf.
"Our findings indicate that where trusts are recording complaints raised by these ‘citizen whistleblowers' they account for a fifth of all cases, so to ignore them presents a huge risk in terms of addressing both the sheer number of individual incidents of poor care and the overall source of feedback they can offer.
She continued: "Whether it is someone visiting a friend or relative in hospital or a courier dropping off a parcel, everyone should be encouraged to help stamp out poor care by raising concerns whenever we witness people not getting the treatment they want, need or deserve."
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