Patients have been forced to travel further and wait longer for urgent care as pressures on the NHS saw a steep rise in emergency departments closing their doors to people being brought in by ambulance.
Concerns about potentially unsafe overcrowding meant that hospital A&E departments temporarily refused to take new arrivals by ambulance on 478 occasions over the three months between December to January.
The figure is nearly double the average of 249 temporary closures per winter over the last three years, according to a report by the Nuffield Trust.
It warned that delays caused by the closures was stopping ambulance crews responding quickly to other urgent calls.
Latest data showed that ambulances reached only 88% of the most serious calls within the target time frame of 19 minutes in January - well below the 95% expected of trusts.
None of the three main ambulance targets for responding to calls have been hit since May 2015.
Richard Webber, national spokesman for the College of Paramedics,said they were "sympathetic" to hospital trusts' concerns over overcrowding but A&E closures caused "significant" increases in travel times to hospital in many cases.
The latest report adds to a picture of an NHS struggling with an increasing care burden and largely flat-lining funding - especially over the winter months when admissions grow.
Five NHS trusts accounted for more than half of all the 493 ambulance diverts reported this winter, with four in the North of England.
The five trusts were: Pennine Acute Hospitals, Northumbria Healthcare, County Durham and Darlington and South Tyneside and Worcestershire Acute Hospitals.
Professor John Appleby, Nuffield Trust chief economist and lead author of the report, said the pressure on emergency services was affecting staff.
He said: "Managers in the NHS and politicians need to make improving the ambulance service's poor morale and its ability to meet targets an urgent priority".
The report said the number of category A calls resulting in an ambulance arriving at the scene has increased by 7.4% year on year, from 2.5m in 2011/12 to 3.3 min 2015/16.
This demand is rising at a faster rate than emergency admissions to hospital and A&E attendances.
An NHSEngland spokesman said: "Currently too many ambulances are dispatched tosimply hit targets rather than attend to those patients most in need.
"This is why we're carefully testing a change to the way in which the services can respond and will make our recommendations known in the coming weeks."