A report revealing that death rates at 12 NHS hospital trusts are above expected levels warns that there could be "another mid-Staffs" as demand for care rises while standards fall.
The Dr Foster Hospital Guide found patient safety is also being risked because hospitals are "full to bursting", with many regularly breaching the 85 per cent limit set in place to protect patients.
The situation has led the Royal College of Physicians to describe the system as "straining to burst" with occupancy running at 88 per cent in midweek during 2011 - 2012.
The Guardian, which has seen the report in full, added that the national level was over 85 per cent for 230 of the 365 days of last year, and more than 90 per cent for 19.
Dr Andrew Goddard, the director of the medical workforce unit at the Royal College of Physicians, which represents hospital doctors, told the Guardian: "If you ask any doctor in this country they would say that the system is straining to burst; particularly in winter, but now it's increasingly happening the rest of the year.
"Hospitals always seem to be full."
The report, part of which has been seen by the Press Association, outlined concerns that there could be "another Mid-Staffs" as hospitals are increasingly focusing on cost of care rather than quality of care.
Each of the 12 trusts fell short on two of four mortality rate indicators - which include deaths after surgery and the deaths of patients who were admitted for minor ailments or "low-risk conditions".
Hospitals always seem to be full Dr Andrew Goddard
"These measures are to be used as a warning sign that poor-quality care may be leading to a higher-than-expected mortality," the report said.
It added: "With the rising demand for care and falling revenues, there are concerns that trusts will focus more (or exclusively) on cost of care rather than quality of care.
"Because of this, there is a fear that there could be another Mid Staffs. Hospital managers must ensure that they do not sacrifice one for the other."
The report also suggests that a shortage of senior doctors working out of hours could be linked to higher mortality rates at the weekends.
However, University Hospitals Birmingham NHS Foundation Trust - one of the 12 trusts named as having higher death rates in two categories - raised concerns about the validity of the Dr Foster indicators.
Dr Dave Rosser, the medical director at the trust, said: "The hospital standardised mortality ratio (HSMR) is widely considered to be unsuitable for use as a comparative indicator between hospitals.
"Dr Foster frequently changes the methodology of the HSMR which, in our opinion, further reduces its credibility as a comparator."
He continued: "In our opinion, the mortality indicator relating to conditions of low clinical risk is deeply flawed.
"To illustrate, one of the patients identified by Dr Foster to be in this category was a patient admitted into one of UHB's specialist services with a condition called toxic epidermal necrolysis, which is known to have a mortality in excess of 50 per cent.
"Under Dr Foster's methodology, this condition is classified as an allergy and therefore treated as 'low clinical risk'. There are many similar examples."
The report, which measures mortality indicators at 145 acute hospitals in England, also found that death rates at three hospitals have been consistently high for three years running.
Buckinghamshire Healthcare NHS Trust, the Dudley Group NHS Foundation Trust and George Eliot Hospital Trust in Nuneaton had high mortality rates three years in a row.
Kevin McGee, the chief executive at George Eliot, said the hospital was working to tackle mortality rates and added that it was pleased with the improvements so far.
"We always knew this wasn't going to be a quick fix; this is very much a journey, both for the trust and the wider health economy," he said.
Meanwhile, spokespeople for the Dudley Group and the Buckinghamshire Healthcare NHS Trust questioned how accurately the report reflected mortality rates.
Authors of the report alerted authorities to problems at the Mid Staffordshire NHS Foundation Trust five years ago - where the deaths rates were also high for a number of years.
Robert Francis QC is currently finalising details of the report into the public inquiry concerning the serious failings at Mid Staffordshire NHS Foundation Trust.
The 12 NHS hospital trusts with higher than expected death rates
Aintree University Hospital NHS Foundation Trust
Blackpool Teaching Hospitals NHS Foundation Trust
Buckinghamshire Healthcare NHS Trust
George Eliot Hospital NHS Trust
Hull and East Yorkshire Hospitals NHS Trust
Medway NHS Foundation Trust
North Cumbria University Hospitals NHS Trust
Northern Lincolnshire and Goole Hospitals NHS Foundation Trust
United Lincolnshire Hospitals NHS Trust
University Hospitals Birmingham NHS Foundation Trust
Walsall Healthcare NHS Trust
Western Sussex Hospitals NHS Trust.