In my latest flight from LHR (LHR-MAD, IB flight but obviously BA gate agents at LHR T5), they were just forcing all the people who boarded first to check their bags, except for those in group 1. I was in group 2, but luckily I didn't have a wheelie but the seemingly invisible Skypak bag, so I was spared. I must say it made for a lot of very angry passengers when they boarded and saw first that the plane was empty and then that the last people to board were allowed to carry as much as they wanted. Of course, a lot of Group 2 passengers just let the agents tag their bags and then brought them into the plane anyway.
I must say they were successful: boarding was finalised and the doors closed 12 min ahead of the scheduled departure, but in the end we still pushed back 9 min late.