Have you considered joining the Volunteer Gliding Squadrons
I looked into this. My 17 year old neighbour was an air cadet at Ternhill, and she dragged me along to find out all about it. You only need to do one weekend day if you want, but you have to be committed to turn up on that day, with only the occasional weekend off. Days are pretty long, starting very early, and often ending at 9pm in the summer. It's all quite formal in some ways, so I hope you don't mind being called sir (or marm), as in "I have control, sir". But they're a nice bunch, the lot I met anyway. They do indeed train you, for free, and with your background and experience, I'm pretty sure they'd take you on. They were going to take me, even though I was over the usual age (40 or 45 max I think), as I had a fair amount of experience...but I got a helicopter instructing job unexpectedly so changed my mind. And you'll help a lot of young people, who don't have a lot of money but want to fly.
Yes, if you want to instruct for free, this is the way to go.
