One word my friend - SEN. Why anyone works in mainstream these days I'll never know. Most schools run by egotistical dickheads ( I deal with quite a few where I live )with unreasonable workloads/ expectations and a seemingly ever increasing number of kids, and parents who couldn't give a fook.
As a bloke with your experience you'd piss your way into a special school. And if you think you'd miss teaching your subject at a high level then just do tuition on the side, you'll have plenty of time.