While still in the RAF and based in West London, I volunteered as an Emergency Responder on the "First Response" scheme. It involved training as an EMT grade 3, and you were expected to man an LAS fast response car at least twice a month to attend grade 1 calls, usually heart attack and stroke victims but also trauma calls, the idea being that you could arrive on scene quickly enough to intervene and hopefully stop the clock on cardiac arrests, allowing a better chance of survival.
I did that for over a year before I had to retire from the RAF and move on further north. I believe it's now called the Volunteer Responder Group. Good gang, and a tough job. I couldn't do medic work full time, an 8 hour shift with an average 8 calls would wipe me out emotionally for a few days.... paramedics and technicians are not paid nearly enough.