Local NHS services could be destabilised by winter flu outbreaks, health experts have warned.
The NHS is "less resilient" to cope with seasonal flu outbreaks as it is operating at a "high level of risk", according to a new report by NHS Providers.
The health service in England is "running at capacity levels beyond the recommended norm" and as a result is "less able to absorb shocks", the authors said.
It is "vital" for healthcare systems to be able to cope with additional demands for care. But the NHS has "seriously reduced resilience", the report adds.
NHS Providers chief executive Chris Hopson warned that "small shocks" risk destabilising local health services.
In a speech to the NHS Providers Annual Conference and Exhibition in Birmingham, Mr Hopson will say: "The service is becoming much less resilient.
"When you run a system under as much pressure for as long as we have been running the NHS, it becomes much less able to absorb the shocks that any health system has to absorb; the winter flu outbreak, the closure of a couple of local care homes due to a CQC inspection or a provider going out of business, a few experienced GPs retiring and being replaced by more risk averse locums or new partners leading to sharply higher referral rates.
"Given the capacity levels at which we are now permanently running our hospital, ambulance, community and mental health services - capacity levels unheard of in Germany, France, Spain and Italy - these small shocks now risk destabilising local health services.
"It's no accident that we have seen some precipitate drops in A&E performance in particular hospitals on particular days - drops that have a clear and demonstrable negative impact on patient experience and patient safety."
NHS Providers, which represents NHS acute, ambulance, community and mental health services, also warned that there is a danger that "quality and access gains made between 2000 and 2010 slowly dissipate".
Its latest report, which draws on a survey from 172 NHS leaders across 136 organisations, also highlights significant concerns about the future of high quality care.
When asked how they would rate the quality of healthcare provided by your local area, two thirds of chairmen and chief executives surveyed said they currently provide high-quality care.
But less than half (46%) said they believe their trusts will be able to provide high-quality care in six months' time.
Many of those surveyed also raised concerns about workforce pressures.
Over half (55%) said they are worried that their trust does not have the right numbers, quality and mix of staff to deliver high-quality care.
Mr Hopson will add: "There is now a clear gap between what the NHS is being asked to deliver and the funding available.
"Seven years into the longest and deepest financial squeeze in NHS history, we have run up a record provider sector deficit. The sector is missing nearly all its performance targets."
He will continue: "We believe the Government should increase funding. And if it won't, it has to honestly accept the consequences - that the NHS can no longer deliver what is being asked of it and the offer has to change."
A Department of Health spokesman said: "As this report acknowledges, the NHS is treating a record number of patients and is making clear progress to balance the books – achievements that wouldn't be possible without our dedicated workforce.
"There are more than 25,800 extra clinical staff on our wards, almost 2,300 more paramedics in our ambulance services and nearly 40% more district nurse training places available since 2010.
"We have also more than doubled the number of trainee doctors working in mental health settings during their foundation programme, and expanded mental health nursing trainee places at a faster rate than any other nursing speciality in the NHS since 2012."
An NHS England spokesman said: "Winter bugs and illnesses always bring more pressure on A&Es but this year hospitals began planning earlier, flu vaccination rates are generally encouraging and we are working far better with senior local council officials in health and social care right across the country."