The National Health Service will struggle to cope with the busy winter period because of high bed occupancy rates and a lack of funding, an NHS research body has warned.
Just 3.6% of patients took up over a third of all bed capacity in acute hospitals in England last year, according to a new analysis of winter pressures on the health service.
The Nuffield Trust, which conducted the research, said the figures help explain why the NHS still suffered a winter crisis last year, "despite receiving extra funding from NHS England of almost £700 million specifically to deal with pressures caused by winter".
It said the patients in the group taking up over a third of bed capacity are "likely to have been frail or elderly people who the system was not ready to return to their own homes or to nursing or residential homes, despite their medical treatment being finished."
The Trust said the four-hour A&E target was repeatedly missed as a result of bed occupancy rates being far higher than the 85% recommended by experts as the maximum.
In turn, this caused the process of treating patients from emergency departments to be slowed.
Last year, an extra £700m was spent as the Government promised the Health Service would be better prepared for winter, and the Nuffield Trust's research said £254m of that winter pot was spent on providing extra beds and staff.
Nigel Edwards, the chief executive of Nuffield Trust, said the lack of extra funding for this year's winter will make it even harder to cope with the busy period.
He said: "These figures show exactly why NHS Trusts found it so difficult to meet the four hour A&E target last winter - despite being able to take advantage of record funding specifically intended to deal with winter pressures.
"Given that there is no extra money for winter this year, they are likely to find it even more difficult to cope in the coming months, especially as almost all Trusts are now in deficit."
Sasha Karakusevic, the author of the report and a visiting senior fellow at the Trust, said: "It is clear that frontline staff across the health and care services are working very hard to do their best for patients.
"But demand is outstripping capacity at present, as it did last winter, and very focused action that addresses the pinch points is needed now."
Commenting on the Trust's assertion that there would be no extra money this year, Sally Gainsbury, the senior policy analyst at the Nuffield Trust, said: "In Autumn and Winter 2014, the Department of Health allocated an extra £700m to local NHS organisations to help them cope with winter pressures.
"This financial year however, this ring fenced funding for winter pressures was halved to £350m and was included in the baseline funding that all organisations received in April, to cover the whole financial year."
She said local organisations were given instructions to spend part of those funds immediately, meaning they will "only have access to a fraction of the funding they had last winter".
Rob Webster, the chief executive of the NHS Confederation, said the health service "must act now" to make sure hospitals are not pushed to breaking point.
"Hospitals under pressure has become the status quo, and this winter is unlikely to be any different," he said. "The solution often clearly lies outside of the walls of our hospitals and into communities.
"Today's analysis reflects that change is urgently needed if we are to build a sustainable health service, especially the way that we deliver care to older people.
"With the commitment of staff and healthcare leaders, backed by investment in the NHS, we have a fighting chance to change how care is delivered.
"This will take time and we must act now to ensure this pressure does not push the system and our hospitals to breaking point."
"By providing care closer to home, building on community services and local voluntary sector partners, where older people need it, we can improve care for individuals and take pressure off hospitals.
"However, we critically need sufficient funding in social care to make this work."
A Department of Health spokesman said: "We gave the NHS £400 million more to help prepare for winter earlier than ever this year and our hospitals are coping well under pressure, with the vast majority of patients being seen within the four-hour A&E target.
"We are committed to the values of the NHS, which is why we are giving the service an extra £3.8 billion for next year on the back of a strong economy."