Patients are at risk in overcrowded hospitals as the NHS struggles to cope with the surge of patients seen in recent weeks, a senior doctor has said.
Prof Suzanne Mason, from the Royal College of Emergency Medicine, described it as a "huge tragedy".
Reports have emerged of patients facing long waits for treatment and being stuck on trolleys in corridors and of ambulances left queuing outside A&E.
NHS bosses said plans were in place to deal with the pressures in England.
This includes the cancelling of non-urgent treatments, such as hip and knee replacements, until the end of January.
Hospitals have also been given the green light to put patients in mixed sex wards.
NHS England director for acute care, Prof Keith Willett, said he had not seen such pressures in the NHS since the 1990s, but he denied the service was in crisis.
"A crisis is when you haven't got in place mitigations and you haven't got a plan to deal with it," he said.
"We've gone into this winter in a way we've never prepared before."
Doctor warns of 'huge tragedy'
But Prof Mason said the measures were "too little too late" as hospitals simply had no beds free and these treatments would have had to be cancelled anyway.
She added: "Patient safety is being compromised – there's no doubt about that. When patients are in crowded emergency departments and staff cannot actually move between patients and provide the basic level of care that's required, then safety is compromised.
"Patients who spend many hours on a trolley – and these are often elderly patients – they are the sickest patients in our department.
"They are much more likely to have a poorer outcome and even die as a result of their experience in the emergency department. And that is a huge tragedy for us in our specialty and that's why we are so desperate to see things improve."
Reports have emerged of serious problems in a number of places:
- Nottingham's Queen's Medical Centre is asking patients to avoid its emergency department as it is on black alert, after seeing 140 patients at its peak on Tuesday evening
- Southend Hospital said it was dealing with an "internal critical incident", which has led them to call in extra staff
- A consultant at University Hospitals of North Midlands NHS Trust apologised for "third world conditions" in his hospital department
- Milton Keynes University Hospital is telling people only to attend for emergency treatment
- Two ambulance trusts in the east and north-east of England have said they are on the highest alert and are asking some of the least serious cases to make their own way to hospital
How has the NHS responded?
As well as cancelling non-urgent care in advance – in previous years it has tended to be done at the last minute – a range of other steps has also been taken, including bringing GPs into A&E units to treat less serious cases.
The NHS response is also being co-ordinated centrally by a new National Emergency Pressures Panel composed of senior doctors and managers.
It was this panel that ordered the cancellation of some non-urgent cases, although treatments for cancer are being prioritised.
Why has this happened now?
The first week of the year is always difficult.
The lack of availability of community services, such as GPs, over the festive period means hospitals tend to see a surge in really sick patients at the turn of the year.
Respiratory illnesses also tend to spike after families have been mixing over Christmas bringing frailer older relatives in contact with young family members, increasing the risk of infections being passed on.
But it is also true to say that this is part of a pattern.
Last January was the worst in a generation and that followed the previous worst the year before.
Commentators have blamed this trend on the squeeze on NHS finances – the health service is in the middle of its toughest cash settlement since it was created.
Since 2010 annual rises have been limited to about 1% on average each year, compared to more than 4% it received previously.
How bad is the situation?
It is very hard to tell. The performance stats – covering waits in A&E, the number of ambulances queuing outside A&E and the amount of operations that have been cancelled – will not be known for a few weeks.
In the lead-up to Christmas, all the indications were that the NHS was in as bad a position as it was the previous winter.
Twice as many patients were waiting for more than four hours in A&E as they should have been, while bed occupancy rates were well above safe levels.
But last winter the really bad spell only lasted a couple of weeks before the pressure eased.
Therefore, it will only be later in January that it will be known whether the NHS is facing a sustained problem.
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