Some coroners in England and Wales are failing to fully investigate hospital deaths, the BBC has been told.
Coroners have absolute discretion over how to conduct inquests, including which evidence to consider and which witnesses to call.
It has emerged that many do not routinely examine medical records.
The government admits there are inconsistencies in the system, but says new legislation will tackle the problem.
Stanley Mack, 77, from Birmingham died in hospital after contracting clostridium difficile in 2008.
His family wanted his death investigated after discovering vital drugs had not been given and routine observations missed.
They hoped an inquest would answer some of their concerns and asked for a number of medical staff on the ward to be called as witnesses.
But the coroner refused and the only doctor called to give evidence was a consultant who had not seen Mr Mack in the 12 days before he died.
The coroner recorded a narrative verdict saying while there were shortcomings in Mr Mack's care, it did not amount to neglect.
The family were so concerned at the coroner's conduct of the inquest that they challenged his decision in the High Court to try to get a new inquest, but lost.
What astonished Mr Mack's family the most was that the coroner admitted he depended to a large extent on the hospital to choose which witnesses they wanted to put forward.
Mr Mack's son Ian said the legal action had so far cost the family £50,000.
"It was entirely illogical to rely on the hospital to choose the right witnesses," he said.
"The system is entirely tilted against the person in the street. It's extremely difficult to get to the bottom of what happens in medical deaths."
File on 4 has discovered other coroners also adopt this approach to witnesses.
There are broader concerns, too, about inconsistency in the way coroners investigate deaths and conduct inquests.
The charity Action against medical accidents has worked with scores of families across England and Wales.
It says there is a huge disparity in the approach of coroners to the disclosure of documents, and that in its experience, many do not routinely obtain or read the medical records.
"If a coroner isn't going to look at those records, then it is very difficult for a family to feel anybody's got to the bottom of what has gone on in the events leading up to their loved one's death," says the head of the charity's inquest project Lisa O'Dwyer.
The government admits urgent reform is needed to make the inquest system more consistent in England and Wales.
It is planning a national charter (pdf) to set out standards of service that families can expect and a new ministerial board to push forward reforms.
"Families should expect a high level of service wherever they live in the country.
"We are taking forward our reforms to ensure bereaved families are provided with the information and indeed the support they need throughout what we appreciate is an emotionally difficult process."