There are "system-wide" problems in the way NHS investigates patient deaths which leave family members in the dark about failures in care, a damning new review has found.
The review by the Care Quality Commission (CQC) highlights how NHS Trusts in England are "immediately on the defensive" with one family member telling the regulator that they had "more courtesy at the supermarket checkout" following the death of their loved one.
The health watchdog identified a string of problems with the investigation process - including a level of "acceptance and sense of inevitability" when people with a learning disability or mental illness died early.
One parent told the CQC: "I was put in a room. I shall never forget what the nurse in the room told me. She said, 'You have got to accept that his time has come.' Bearing in mind my son was just 34 years old."
Where deaths may have been prevented, NHS Trusts carry out investigations to establish accountability, learn from mistakes and to explain to families what went wrong.
But the CQC said grieving families were not being included or listened to in official investigations into patient deaths.
They were also left without clear answers as to what happened.
One family member told the CQC: "You're viewed as a pain in the neck really, it's a bit like if you keep complaining about the washing machine but the machine is out of warranty.
"I've had more courtesy at the supermarket checkout than I've had at the trust."
Meanwhile, the NHS is also missing opportunities to learn from patient deaths. This means similar tragedies may be repeated in the future, CQC warns.
Not one NHS trust was "getting it right", the CQC's chief inspector of hospitals Professor Sir Mike Richards said.
Sir Mike said: "We found that, too often, opportunities are being missed to learn from deaths so that action can be taken to stop the same mistakes happening again.
"Families and carers are not always properly involved in the investigations process or treated with the respect they deserve.
"We found this was particularly the case for families and carers of people with a mental health problem or learning disability which meant that these deaths were not always identified, well investigated or learnt from.
"While elements of good practice exist, there is not a single NHS trust that is getting it completely right currently.
"Investigations into patient deaths must improve for the benefit of families and importantly, people receiving care in the future.
"This is a system-wide problem, which needs to become a national priority."
The foreword of the report adds: "We found that the level of acceptance and sense of inevitability when people with a learning disability or mental illness die early is too common.
"There can be no tolerance of their deaths being treated with any less importance than other patients."
The assessment, which paid particular attention to deaths of patients with mental health conditions and learning disabilities, is based on evidence from visits to 12 NHS trusts, a national survey of all NHS providers and interviews and discussions with more than 100 families.
The authors examined 27 death investigations and found that only two of the reports contained a "satisfactory response" to the family or carers of the person who died.
Loved ones were not always informed or kept up to date about investigations - often causing them further distress.
Families described a poor experience of investigations and told the CQC they were not consistently treated with respect, sensitivity and honesty.
In some cases, family and carer involvement was "tokenistic", the CQC said.
Meanwhile, trust board members often do not interrogate or challenge information about patient deaths effectively.
The CQC also expressed concern that trusts did not share what they had learned from errors.
"This means that mistakes may be repeated," the report added.
The investigation was commissioned by Health Secretary Jeremy Hunt following the review into the death of Connor Sparrowhawk, who died while being cared for at Southern Health NHS Trust.
The family of the 18-year-old, who had a learning disability and epilepsy, raised concerns about the way his death was being investigated.
Following their campaigning, an investigation concluded that the teenager's death was entirely preventable.
Commenting on the report, Professor Dame Sue Bailey, chairwoman of the Academy of Medical Royal Colleges, said: "Put simply, we have consistently failed and continue to fail too many of the families of those who die whilst in our care.
"We must now ensure we rapidly put in place system-wide changes so that NHS trusts always treat families as equal partners in a consistent manner with humanity, honesty and common decency when deaths occur."
Parliamentary and Health Service Ombudsman Dame Julie Mellor, added: "Time and time again we find NHS investigations into deaths inadequate, causing further suffering to families who have lost their loved ones.
"This report is a golden opportunity for NHS leaders to learn from mistakes and encourage an open, honest working environment where NHS staff do not fear reprisals."
Commenting on the report, Mark Winstanley, chief executive at the charity Rethink Mental Illness, said: "The findings of this review make for some very bleak reading.
"Not only are people with mental illness still dying 20 years earlier than the rest of the population, but lessons are not being learnt about why this is happening, which is often down to poor health monitoring and responsiveness by the NHS and the dismissive attitude of some health professionals towards people with severe mental illness.
"Through this review we've heard that many of these deaths are not recorded as serious incidents and therefore not investigated and, as a result, no lessons can be learnt."
Mr Hunt is expected to accept all 18 recommendations set out in the report in a speech to the Commons on Tuesday.
These include setting a national standard into how NHS trusts investigate deaths and appointing a senior board member at each organisation to lead on patient safety.
Health officials will also publish information on how many deaths could have been prevented at individual NHS trusts.