Death rates at 12 NHS hospital trusts in England were alarmingly high last year, according to an influential report.
The number of patient deaths are above expected levels at the 12 trusts, the Dr Foster Hospital Guide found. Patient safety is also being risked because hospitals are "full to bursting", with many regularly breaching the 85% limit set in place to protect patients.
Figures shows that in 2011-2012 occupancy was running at 88% in midweek, while averaging 90% for 11 of the 12 months, excluding quiet periods including Christmas,
The Guardian, which has seen the report in full, added that the national level was over 85% for 230 of the 365 days of last year, and over 90% 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, outlines 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".
The report states: "These measures are to be used as a warning sign that poor-quality care may be leading to a higher-than-expected mortality. 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."
However, University Hospitals Birmingham NHS Foundation Trust (UHB) - 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, medical director at the trust, said: "The HSMR (Hospital Standardised Mortality Ratio) 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."
The 12 hospital trusts where the number of deaths are higher than expected in two of the four mortality indicators are: 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.