London Air Ambulance has launched a fundraising appeal as it races against time to replace its two helicopters.
The charity said it needs to raise £15 million by 2024 to replace both aircraft, which are becoming increasingly difficult to maintain.
London Air Ambulance, which gets 89% of its funding from public donations, is launching the campaign, Up Against Time, on Tuesday.
Volunteers, staff and off-duty crew from across the organisation will be collecting donations on the streets of London throughout the morning, it said.
The charity is also looking to raise awareness by publishing new polling data as part of the campaign launch with research finding that only 38% of Londoners know the service is primarily funded by public donations.
Just over a third – 36% – said they think the service is funded by the NHS or central government.
London Air Ambulance said it found that 51% believe the main purpose of its helicopters is to collect patients from the scene of an accident and take them to hospital.
But the organisation said its role includes getting medics to the scene quickly so they can provide complex treatment to critically injured patients with life-threatening or life-changing injuries, who do not have time to make it back to hospital.
The survey found that 33% of respondents do not know that LAA medics carry out procedures such as open chest surgery, blood transfusions and reinflating collapsed lungs at the scene.
London Air Ambulance medics saved the life of medical student Matt Gunnee, 27, who was hit by a car in West Kensington in 2016.
The team placed Mr Gunnee into an induced coma at the scene before he was taken to St Mary’s Hospital in Paddington with a broken skull, jaw, eye socket, femur and knee ligaments.
He also suffered a life-threatening brain injury which required emergency surgery but he made a significant recovery by 2018 and was able to return to medical school.
Meanwhile, Claire, who did not give her surname for legal reasons, was given an emergency anaesthetic and blood transfusion at the scene after she was stabbed repeatedly by her ex=partner in her home while she was asleep.
London Air Ambulance medical director Dr Tom Hurst said: “Both Claire and Matt have made an incredible recovery and it is amazing to see their resilience and bravery.
“In both cases, their injuries meant that it was absolutely critical that we were able to get to them quickly and treat them on scene; there was simply no time to get to hospital.
“Claire and Matt have their whole lives in front of them and their stories could have been very different.”
Last year, London Air Ambulance assisted 1,714 patients at the scene – an average of five a day.
Dr Hurst said: “When patients are so seriously injured there is no time to reach hospital, our medics give life-saving treatment at the scene – like open chest surgery and blood transfusions.
“But we’re a charity, and without public support we wouldn’t be able to reach our patients in time to help them.
“Right now, we have an urgent need to replace our helicopter fleet – the current helicopters are becoming increasingly difficult to maintain.
“It’s only with the backing of the public that we can continue to serve all those who live and work in London when they need us most.”
Those wishing to donate can do so at https://fundraising.londonsairambulance.org.uk/event/big-city-collection or via the online form at https://www.londonsairambulance.org.uk/up-against-time-appeal.