I live in the UK under ILR and have never acquired the biometric pass. I travel every week, more or less, and never travel with my stamped passport (long expired). Checking in is rarely an issue, if ever, although I am on a commonwealth passport. The only issue I’ve ever had was as Madrid, when they would not let me check in, and I did not happen to have any other flights in my bookings. This was solved by purchasing a ticket out of the UK a week later, immediately cancelled. Perhaps I am blasé as I use the e-gates, but I do find out-station staff less fastidious, with UK border staff able to access the system. Just my experience.