Another underused supply of instructors is the older generation who are retired or semi retired from having flown for a lifetime....
......I don't know what it is like in Britain but in Canada our regulator makes it to difficult to get an instructors rating ( or to renew one ).
My personal opinion is they do not want to have to deal with people who understand how to fly and how to survive flying.....what they want is mindless submission to their ideas of how to teach flying....
It is easier for them to control those who have been brain washed than try and B.S. those who understand the subject.