I was told, to be selected and pass it helps if you are member of the famous Heathrow goat riders club, ie a Mason.
There is a past Balpa magazine article on this interview.
Published one Christmas it delt with the required techniques ( all the questions asked, and their model answers) to pass the training Capt interview at BA.
I recall the answer to the question, What is our company fuel policy and how do you feel about it? was "I feel it is really very important and probably with someone big like, Norwich Union."
Be aware you could end up "different" after a few years as a trainer and become all of the things you hated in trainers when you were a happy go lucky line pilot.