Around one in seven ambulance patients in England are still waiting more than an hour to be handed to A&E teams at hospitals, with nearly one in three waiting at least 30 minutes.
The numbers are higher than at any point last winter.
Health experts said the delays show the NHS is facing “the toughest pressures since modern records began” and is struggling to create space for new arrivals.
A total of 23,894 handover delays of half an hour or longer were recorded across all hospitals trusts last week, according to NHS England.
This was 31% of all arrivals by ambulance, the same level as the previous week.
The proportion stood at 23% at the beginning of December 2021 and 11% at the start of December 2020.
This was also unchanged on the previous week, but up from 10% a year ago and just 3% in December 2020.
NHS trusts in England have a target of 95% of all ambulance handovers to be completed with 30 minutes, with 100% to be completed within 60 minutes.
Danielle Jefferies, of health charity The King’s Fund, said the figures show “an NHS bursting at the seams” as it attempts to meet sharply rising demand while keeping patients safe.
She continued: “Improving ambulance delays has been a government priority for some time, but today’s numbers show that one in seven ambulances are delayed by more than an hour as they wait for stretched A&E teams to assess patients.
“Problems at the hospital front door are indicative of issues at the back door. People are being stranded in hospital because of a long-term lack of investment in social care and NHS community services.
“It is easy to become numb to dire NHS performance figures, but the health service really is facing the toughest pressures since modern records began.”
Analysis of the data by the PA news agency shows that, among those trusts reporting at least 500 ambulance arrivals last week, the highest proportion of patients waiting over an hour to be handed over was 56% at Royal Cornwall Hospitals (361 out of 639 patients).
This was followed by University Hospitals of North Midlands at 52% (384 out of 739 patients), Northern Lincolnshire & Goole also at 52% (335 out of 643), University Hospitals Bristol & Weston at 42% (339 out of 805), Gloucestershire Hospitals at 41% (308 out of 756) and University Hospitals of Leicester at 38% (386 out of 1,023).
They may have been moved into an A&E department but staff were not available to complete the handover.
But the high level of delays reflects the struggle faced by hospitals in finding space for new arrivals.
Separate NHS figures show an average of 13,358 hospital beds per day last week in England were occupied by people ready to be discharged.
This is broadly unchanged on the previous week’s average of 13,364, but is 27% higher than the number in the first week of December 2021.
Sarah Scobie, deputy director of research at the independent health think tank The Nuffield Trust, said: “NHS hospitals are desperately struggling to get patients in and patients out fast enough, and the situation continues to deteriorate as the temperature drops and we head into the most challenging winter months.
“Data shows the severe impact on staff with these delays, resulting in the loss of an average of 3,400 hours of ambulance staff time per day which could be used for patient care.
“Ambulances are one of the most visible and vital cogs of the emergency care machine, and it is becoming more painfully visible that they are under severe strain. The Government has confirmed additional funding to tackle the delayed discharges behind some of these problems, but it is far too late in the day to have a meaningful impact this winter.
“On top of confirmed ambulance and nurse strikes, unfortunately winter will keep getting harder for patients and NHS staff.”
Nursing staff will take industrial action in England, Wales and Northern Ireland on December 15 and 20, while ambulance workers in England and Wales will take action on December 21.