So basically, if you don't pass everything as the first try, you don't get an instructorjob
Thats not true actually. We are all human and make mistakes. Its the manner of your conduct, and the way you interact with other instructors and students that can make or break it for you.
I'm sure you will be fine. Dont worry about it, just concentrate on getting your ratings first.
Take care M.
PS: Not sure about instructing at UK base, think its only CPL and IR there at the moment, but have a word with the school.