Hospitals are struggling to cope as the number of inpatient beds continues to be slashed across the health service, an influential think tank has warned.
A report from the King's Fund found that the health service in England is facing increasing pressure as it goes into the winter months.
Last winter, hospitals across the UK declared major alerts and closed their A&E doors, with an average of more than 90 per cent beds full across the service.
At various points, hospitals had around 96 per cent of their beds full and regularly went above 95 per cent. Anything above 85 per cent increases the risk to patients from infection and is considered unsafe.
The new study says that with hospitals already full to capacity, STP proposals in some areas to cut beds are "undesirable and unachievable".
The number of NHS hospital beds in England has more than halved over the last 30 years, from around 299,000 to 142,000.
The report said this is partly because more patients with mental illness and learning disabilities are cared for in the community and patients generally need to spend less time in hospital than in the past.
But it warns that the NHS "now has fewer acute hospital beds per person than almost any other comparable health system".
And it points to a growing shortage of beds as hospitals struggle to cope with increasing numbers of patients with more complex conditions.
It said: "Today there are signs of a growing shortage of beds.
"In 2016/17, overnight general and acute bed occupancy averaged 90.3 per cent, and regularly exceeded 95 per cent in winter, well above the level many consider safe.
"In this context, proposals put forward in some sustainability and transformation plans to deliver significant reductions in the number of beds are unrealistic."
The report said cutting beds relies on people being cared for closer to their homes and in the community but current intermediate care - the services to support patients leaving, or at risk of going into, hospital - is only sufficient to meet around half of demand.
Shadow health secretary Jonathan Ashworth said: "The Tories' refusal to give the NHS the money it needs has put services across the country under strain.
"It means hospitals running over safe occupancy levels throughout the year. Patients deserve better.
"It is essential that decisions about bed numbers are driven by what is best for patients and local communities, not by underfunding."
An NHS England spokeswoman said: "Hospitals have said that they are planning to open up more than 3,000 extra beds this winter and, in addition, work is under way to free up to 3,000 more by improving the availability of community health and social care.
"We have also introduced an explicit test to prevent inappropriate bed closures while recognising that the right number of beds in any geography will partly depend on the age and number of patients in that area, the availability of alternative community services and also the level of the NHS budget that parliament requires local areas to operate within."
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