Ambulances are failing to reach dying and seriously-ill patients fast enough as the service creaks under the strain of high demand, according to a report.
Only one of the UK's 13 ambulance services, the Welsh Ambulance Service, is meeting the target to reach patients with life-threatening conditions within eight minutes, a BBC investigation has found.
Freedom of Information requests by the broadcaster found more than 500,000 hours of ambulance crews' time in England, Wales and Northern Ireland was wasted waiting at A&E to hand over patients to hospital staff.
Dr Mark Holland, president of the Society for Acute Medicine, said the "significant strain" on the NHS was due to the Government's failure to accept the social care crisis.
He said: "The Government has continuously failed to acknowledge the scale of the crisis in social care and the record numbers of delayed discharges in our hospitals as a result - a significant factor in the build-up of pressure on our hospitals.
"Having the support and infrastructure in place to discharging medically-fit patients safely is central to releasing pressure on emergency departments, acute medical units and ambulance services.
"It is essential that clinical and political leaders ramp up the pressure and hold the Health Secretary and government to account on this issue before it is too late."
NHS England's ambulance lead, Professor Jonathan Benger, said the rising number of calls the service received was a major factor in the delays.
He told the BBC: "In the face of rising demand it is not surprising we are having difficulty meeting these targets. It is time to look at the system."