Doctors fear that cases of cancer have been regularly missed in a scandal over botched diagnoses which goes back a decade.
An NHS inquiry is examining more than 3,000 tissue samples after medics expressed concerns about misdiagnoses, including cases of patients who died following failures to detect their disease.
The investigation is being held behind closed doors and none of the evidence has been made public.
Documents seen by The Sunday Telegraph disclose that four doctors from different hospitals in Bristol expressed concerns that critical and repeated blunders were being made by a laboratory at one of the city’s hospitals.
Cases include a 55-year-old woman who died three years after an NHS biopsy failed to detect breast cancer.
Jane Hopes, who was a senior NHS manager in Bristol, was never told that doctors at the hospital where she worked believed a critical error had been made in diagnosing a lump in her breast as benign, when the disease was at its early stages.
Her bereaved family told this newspaper that they had not been told about the concerns, or that the case was part of a major investigation which began last June.
Mrs Hopes’ case was one of 26 in which doctors had raised specific concerns about misdiagnosis.
Submissions by specialist doctors said other serious errors had caused the death of a child, while other patients were treated for the wrong disease, received a late diagnosis, or were given needless toxic treatment.
The consultants wrote to NHS bosses in 2007, and again in 2008, expressing concerns about the standards of pathology at Bristol Royal Infirmary (BRI) and citing allegations of misdiagnoses dating back to 2000.