More than 900,000 emergency calls for ambulances were answered without paramedics last year, new figures reveal ahead of what could be one of the busiest nights of the year for the service.
Emergency care assistants, or other non-fully qualified paramedics, attended at least 939,893 incidents alone in the year 2016/17 in England, according to an investigation by GMB union.
General secretary Tim Roache called for additional support for "overstretched" services, but ambulance trusts defended frontline clinical support staff as "highly-skilled and valued" members of the workforce.
The figures come as emergency services prepare for Mad Friday, the last Friday before Christmas, when people are expected to fill pubs, bars and clubs across the country.
Mr Roache said: "Proper support for our overstretched ambulance services is literally a matter of life and death.
"GMB members are performing miracles every day but the system is failing because funding just hasn't kept pace with demand."
He added: "This must be a wake-up call for Jeremy Hunt. It is vital that our ambulance services are given the additional resources they desperately need."
South East Coast Ambulance Service (SECAmb) had the highest number of non-paramedic responses out of the nine trusts which replied to GMB's Freedom of Information request, with 190,813 incidents last year.
North West Ambulance Service (NWAS) revealed 155,902 calls were answered by emergency care assistants or non-fully qualified paramedics, of which 650 were graded as the most time-critical incidents, GMB said.
North East Ambulance Service recorded the fewest, with 53,105 incidents, while East of England Ambulance Trust did not respond to the request for information.
A spokesman for SECAmb said all crews could request paramedic back-up if necessary when they arrived at a call.
He said: "Clinical support staff, which make up 48% of our frontline workforce, are highly-skilled and valued members of our workforce and provide excellent care to our patients every day.
"These figures should be seen in the context of the more than 700,000 emergency responses we carry out each year where ambulance crews of varying clinical grade work alongside each other to treat patients."
A spokeswoman for NWAS said: "All of our crews have a wide range of support available to them including clinical support hubs within our emergency operations centre manned by senior paramedics, who are on hand at all times to give enhanced clinical advice to both Emergency Medical Technicians and paramedics if needed.
"We always work with the patient's best interest at heart and in life-threatening situations, the nearest available crew will be sent to start care as soon as possible."
Ambulance services are expected to be extremely busy on Mad Friday and revellers have been urged to drink responsibly and think before dialling 999.
Ged Blezard, director of operations at NWAS, said: "The service is incredibly busy and we don't have spare paramedics and ambulances to deal with the extra calls which occasions such as Mad Friday present us with.
"This means that we really need people to take some responsibility for their own safety during this busy period.
"In genuine life-threatening emergencies, time matters. If people stop and think about their actions and try not to have one too many during the festive period, they can help us to get to the vulnerable and very poorly people that really need us - it could be one of their relatives relying on us."
London Ambulance Service (LAS) said more crews and control room staff would be on duty across the weekend, including 16 extra ambulances every hour on Friday.
Martin Flaherty, managing director of the Association of Ambulance Chief Executives, welcomed "the underlying call for more funds for ambulance services which is a core part of the GMB message" but said there was disappointment at "the apparent lack of support for non-paramedic clinical ambulance staff".
"Our emergency medical technicians make a massively positive input to patient care and to the NHS as a whole, and we are certain the public will feel the same," he added.
A Department of Health spokeswoman said: "We're helping ambulance staff workloads by recruiting 2,600 more paramedics since 2010, as well as training record numbers of new paramedics."