I agree with sashh. My main concern would be people who are frail or vulnerable not wanting to call an ambulance when there is a legitimate reason to.
I've been transported to hospital by an ambulance once when I didn't need it (I didn't have a whole heap of choice - I was unconscious, but it could have been avoided if any one of the people I was with had the confidence to put me in recovery and elevate my legs until I was awake again.)
Once I didn't call an ambulance when I was in the early stage of shock. I needed rehydration, so was justifiably in hospital, though I should have been able to prevent the shock happening. I'm glad I didn't call an ambulance for that one. It was bad enough that I'd let myself get so ill in the first place, though my Dad who gave me a lift was really cross with me for not calling one. That was a fun journey.
I also organised my own transportation when DD was ill. That's the one that really scares me. She had septicaemia and if our car had been stopped in traffic, if my Mum had decided to take a shower before coming out to pick us up, then it would have been too late. She was literally in treatment and fighting for her life within half an hour of getting to the hospital. 45 minutes would have been too late.
The problem is, I've almost been over-educated in not calling an ambulance unless you might die that second. I wasn't aware of how quickly a 10 month old could start to fail. That occasion was already tough, because I was overruling the decisions made by the GP who had seen her three times that week and written it off as just a cold. If I had the extra concern of 'and also, they might fine us...' then we're wasting yet more precious minutes.
Both times DS needed to go to A&E to be checked out, he was very much walking wounded, so it was fine to be on a bus.
An additional issue that might make people favour an ambulance is that parking at hospital is nightmarish and expensive. I have been in the position of simply not having taxi money (and digging under cushions for bus fare), and knowing that there wouldn't be any place for me to park a car at the hospital. The stress of having a sick child in the car, while simultaneously looking for a place to park is too much. Both times DS had to go to hospital, we've gone on the bus - a trip that takes an hour. Not comfortable for him, but my attitude is that if he can manage it, he should (poor boy).
I'm not saying people shouldn't drive - I'm saying that parking at hospitals needs to be addressed, and this might reduce some of the load on the ambulance service.
So I think there should be something to prevent misuse, but not necessarily an automatic fine. Or perhaps there could be fines, but not for people over a certain age, or for babies under, what, 1? 2? Or with an permanent condition, or a disability?
Basically, a system that doesn't penalise those who are vulnerable.