OP - I think you're underestimating how difficult teaching is. It's virtually impossible to teach well without training. And I'm definitely a much better teacher than I was when I started out 16 years ago. You wouldn't expect to just rock up in theatre and be able to perform an operation, even if there are shortages of surgeons, or, if you had no computer programming experience, just get a job with an IT company and start programming - it's the same with teaching.
I know you probably think you know how to teach, but believe me, you have no idea. Head teachers know this, hence why, even in academies, they only take on qualified teachers.
Even people on PGCE courses and NQTs often drown in the job and end up leaving - and they are basically thrown in at the deep end, but at least it's not on a full timetable.
Teaching is so, so hard, and the hours are silly for the first few years, until all your lessons are planned, and you can reuse them. And very often syllabi change, or you have to step up and teach a different subject/year group, then the planning starts from scratch again. The kids can be complete shits some days, bullying by management in some schools is shocking. I've seen many a teacher sobbing in the staffroom due to both those factors.
I'm not trying to put you off teaching altogether, because there are lots of pros to the job, but believe me, it is not easy, and you need training, or you'll end up having a breakdown.