The number of patients who are forced to wait for more than four hours in accident and emergency departments before being treated has reached its highest level in a decade, a new report suggests.
In the last three months of 2012, 232,000 patients waited more than four hours in A&E - an increase of 38% over the previous quarter.
Experts at The King's Fund said that between October and December the proportion of patients waiting more than four hours was at its highest level since 2003.
Researchers said that as financial pressures continued to "bite hard" on the health service there was growing pressure on emergency care.
So-called "trolley waits" - where patients who attend A&E and need to be admitted to hospital have to wait before they are given a bed - were also at their highest rate since the same period in 2003.
The latest report by the influential think tank suggests that health and social care providers are "pessimistic" about the financial outlook of their organisations and some are concerned that the quality of patient care has suffered as a result.
Two-thirds of 48 NHS finance directors and 58 directors of adult social care services surveyed said they were concerned about the financial outlook across the local health and social care system in 2013. A third of NHS finance directors said the quality of NHS care in their area had deteriorated over the past 12 months.
And half of social care directors said they thought the quality of services they commissioned had worsened in the past year, with a third fearing they would have to reduce services over the coming year.
"The NHS faces unprecedented financial pressures, and there are growing worries that patient care will suffer," Professor John Appleby, chief economist at The King's Fund said. "For social care, it will be increasingly difficult for councils to make further savings without directly cutting services or affecting quality. Health and care services have coped well until now, but it is clear that many organisations expect things to become much more difficult over the coming year."
Mike Farrar, NHS Confederation chief executive, said: "Despite huge efforts to maintain standards of care and finances, NHS leaders are increasingly concerned about the pressures mounting on their organisations and the knock-on impact of reductions in funding for local government services. The findings of the Francis inquiry reinforce the fact that we must keep the focus on patients first and foremost."