“Given current performance and the risk to patient safety, we must however press to identify further solutions to eliminate all handover delays,” said the letter from Prof Stephen Powis and Pauline Philip, the national director for emergency and elective care.

Patients who arrive at hospital by ambulance are supposed to be handed over from paramedics to hospital staff within 15 minutes.

Martin Flaherty, the managing director of the Association of Ambulance Chief Executives, reported 35,000 handover delays of at least an hour outside hospitals last month, compared with 4,700 in April.

Latest NHS data for England shows the busiest September on record. Major A&Es treated more than 1.39 million people during September, the highest ever for the month.

Ambulances responded to a record 76,000 life threatening callouts, while 999 took nearly one million calls in September.