If my powers of deduction are correct, you are on the BA522 at 18.35 and he is on the BA520 at 17.10. I looked up Avios redemption options - your flight shows J1, his shows J1 Y9. So why don't you pay a small fee to just have him move to your flight, or if your ticket is a single with nothing riding on it, if they won't change it at the airport, throw it away and blow a few miles and book yourself onto his? You have to be ticketed 1h before take-off, I think, so you'd have to be there quite early.