I was annoyed on a recent trip connecting to LHR for a TATL connection, that as a GCH boarding straight away with group 1 that I was asked to put my backpack, which whilst medium sized was plumply packed, under the seat in front of me. As my only piece of cabin baggage. Surely part of priority boarding is having access to the over head bins for your larger item. Of which this was mine. I could, obviously have packed into a larger cabin bag and had it accepted, but that wouldn’t have helped later on when manoeuvring my larger still, but still cabin sized suitcase that I chose to check in the hold.