Ambulance services are under intense pressure, with record numbers of callouts and the most urgent, category-one, calls last month.
BBC Two's Newsnight programme spent from 08:00 to 20:00 on Monday at six hospitals with the longest delays handing patients over from paramedics to accident and emergency staff.
This should take 15 minutes or less - but crews often wait many hours and sometimes whole 12-hour shifts, with ambulances queuing outside unable to respond to other emergency calls.