Data published by NHS England on hospital pressures show that 94.5% of general and acute hospital beds in England were occupied in the week from 27 November to 3 December.
Hospitals are told to aim for a rate of 85% bed occupancy because research has shown that 'risks are discernible' above this threshold - but just four out of 137 hospital trusts in England reported bed occupancy below the target over the past week.
Analysis by GPonline found that at 115 hospital trusts, a total of 90% or more beds were occupied - a level likely to trigger 'regular bed shortages and periodic bed crises'.
Two hospitals - James Paget University Hospitals NHS Foundation Trust and the North Middlesex University Hospital NHS Trust - reported 100% bed occupancy throughout the week, and NHS England reported that 11 A&E departments were forced to divert patients to other hospitals.
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GPC chair Dr Richard Vautrey said: 'With a bed occupancy rate like that, it can become unsafe for patients and increase problems for hospitals. It becomes harder to admit patients, and puts pressure on GP practices to manage more in the community.'
Data showing the extent of pressure NHS hospitals are under comes just days after GPonline revealed that more than two thirds of GPs expect their practice to struggle to cope this winter. Nine out of 10 said they expected the NHS as a whole to struggle.
NHS England has decided not to publish details of hospitals declaring high-level alerts - often referred to as 'black alerts' - this winter. A spokesman said this information would not be made public, but instead used 'operationally'. A newly established 'national emergency pressures panel' will 'identify and act' when areas face extreme pressure.
NHS England said it will publish 'more data than in previous winters, including A&E closures and diverts, bed availability and occupancy rates and ambulance handover delays' through this winter, along with updates on flu and norovirus.
Cold weather alert
NHS England has also warned health service staff to expect temperatures to drop from Thursday - issuing advice that there is a 90% chance of severe cold weather, ice or snow in parts of the country, potentially putting vulnerable patients at risk and disrupting NHS services.
Dr Vautrey said the impact of hospital pressures on GP practices changed 'day by day' and warned it was difficult for practices to keep up with the situation at their local hospital. He added that warnings from hospitals not to refer unless absolutely necessary were unhelpful because practices do not take referral decisions lightly.
An NHS England spokesman said: 'The NHS has prepared for winter this year more intensely than ever before, developing robust plans to manage expected increased pressures, as well as create contingency plans to cover exceptional surges in demand.
'The public can continue to play their part by making sure they have their flu jab and by using local pharmacies and NHS 111 for medical advice, alongside other services.'
Flu levels remain relatively low in England, but GP leaders have warned that a significant outbreak this winter could tip the NHS into crisis because of existing high levels of pressure on the service.
BMA chair Dr Chaand Nagpaul said the hospital data showed 'a service under huge pressure with little or no spare capacity as the NHS approaches its busiest time of the year'.
'The concern is that that if there is a serious flu outbreak or cold snap the system would really struggle to deal with a spike in demand.
'The extra cash promised in the budget for the NHS this winter may alleviate some short-term pressure but will not address the long-term needs of the NHS and it’s a sticking plaster solution. NHS staff in our GP surgeries and hospitals are working flat out to treat patients quickly and efficiently, but they are under unsustainable pressure.'