The NHS is at "breaking point", with a decline in the number of hospital beds leading to delays in admissions and cancelled operations, the British Medical Association claimed.
The report, based on official statistics, found in the first week of January this year, almost three-quarters of trusts had a bed occupancy rate of over 95% on at least one day.
It said in November 2016, 14.8% of patients spent more than four hours waiting for a hospital bed, having been seen in an A&E department.
The document was seized on by opposition politicians, with Labour saying it was a "wake-up call which Theresa May must not ignore" and the Liberal Democrats warning the situation was becoming "intolerable".
BMA chairman Mark Porter said: "The UK already has the second lowest number of hospital beds per head in Europe per head and these figures paint an even bleaker picture of an NHS that is at breaking point.
"High bed occupancy is a symptom of wider pressure and demand on an overstretched and underfunded system.
"It causes delays in admissions, operations being cancelled and patients being unfairly and sometimes repeatedly let down.
"The delays that vulnerable patients are facing, particularly those with mental health issues, have almost become the norm and this is unacceptable.
"Failures within the social care system are also having a considerable knock-on effect on an already stretched and underfunded NHS.
"When social care isn't available, patients experience delays in moving from hospital to appropriate social care settings which damages patient care and places a significant strain on the NHS.
"In the short term we need to see bed plans that are workable and focused on the quality of care and patient experiences, rather than financial targets.
"But in the long term we need politicians to take their heads of out the sand and provide a sustainable solution to the funding and capacity challenges that are overwhelming the health service."
But Department of Health officials disputed some of the report's key findings, insisting changes in the way data were recorded meant historic figures could not be compared to the current situation.
The BMA report said the number of overnight beds in English hospitals fell by a fifth between 2006/7 and 2015/16.
And according to the analysis, in 2000 there were an average of 3.8 beds per 1,000 people, but this had dropped to 2.4 beds by 2015.
The Department of Health said figures from before 2010/11 included NHS-provided residential care beds and were compiled on an annual basis, while the more recent figures were published quarterly and only included beds under the care of consultants.
A spokesman said: "This analysis is inaccurate, the figures come from two different time periods when the way of counting beds was different, and so they aren't comparable.
"Our hospitals are busier than ever but thanks to the hard work of staff, our performances are still amongst the best in the world.
"We have backed the NHS's own plan for the future with an extra £10 billion by 2020."
The BMA said the figures in the report had been adjusted to exclude geriatric beds, while even the current method of data collection shows a decline in the number of beds.
In the first quarter of 2010/11 there were 144,455 available beds but in the same period in 2016/17 the figure was 130,774 - a fall of almost 9.5%.
Shadow health secretary Jonathan Ashworth said: "Thanks to Tory mishandling of our NHS, patient numbers in hospitals are now routinely above the levels recommended for safety.
"The shameful reality is this overcrowding puts patients at risk and blows apart ministers' claims to be prioritising safety."
He added: "This Government's mismanagement is failing our NHS and failing patients.
"The Prime Minister must wake up to this crisis and ensure that the NHS and social care have the funding and support needed in the Budget next month."
Lib Dem spokesman and former health minister Norman Lamb said: "Chronic bed shortages should be the exception not the rule.
"The situation is getting intolerable, with more cancelled operations, longer delays and those with mental health issues being systematically let down.
"The Government is failing to properly fund the NHS and patients are paying the price.
"Ultimately, we could reduce the need for hospital beds by improving preventive care. But cutting both preventive services and beds leads to disaster.
"That is what we are now witnessing."
A NHS Improvement spokeswoman said: "The NHS has been under real pressure this winter, as it copes with a surge in demand for emergency services the knock-on effects are felt throughout our hospitals.
"Our hospitals are extremely busy but we are working tirelessly alongside providers to help them manage and to support more efficient use of the number of beds available."
The BMA's report comes ahead of the publication of NHS Improvement's figures for the third quarter of 2016-17 which are expected to show the parlous state of trusts' finances.
NHS Improvement's chief Jim Mackey has acknowledged trusts will miss the £580 million deficit "control target" and forecasters have predicted the combined black hole in their finances could reach nearly £1 billion by the end of the year.
A spokeswoman for NHS England said: "Modern treatment advances such as minimally invasive surgery, fast acting anaesthetics, and medicines taken at home mean the length of time patients spend in hospital has been falling in all western countries.
"The NHS is highly efficient overall, but there are still meaningful differences in discharge practices and community support across England."