God and what about mental health care? How much would the ambulance service and A+E be helped if there was a proper approach to triaging and treating mental health patients in the community (as opposed to a hospital ward)
It's going to be beyond "a significant figure".
At some point, public speculation on how much funding the NHS needs always seems to rely on "if all these ill, worried and panicking people in pain make rational, well-considered decision and go to the correct clinical provider in the first place and no-one seeks treatment inappropriately for a non-issue, we can make do with only £x billion".
And how are we going to do that? So much of the NHS's workload now is the mentally-ill, elderly people who are developing dementia and so on. We can't build a system that relies on these users contacting the correct provider by themselves, and patiently waiting indefinitely by the underfunded specialist clinic.
The services need to be properly funded, and people need to be funnelled into them before they ever end up in A&E.
Otherwise, what? Are we going to wave a wand and make everyone medically qualified enough to triage themselves? Magically eliminate the effects on decision-making of pain?