I have noticed it in LHR recently, I never use check in desks but I did see that process. I've always found priority boarding to be of limited value in general on most airlines I fly. It seems if you want priority boarding just join that queue, very rare I see anyone challenged or checking and for sure some people just chance it with success. US airlines seem to be better at enforcing it IMO but maybe they are more demanding.
Besides I thought you were leaving us for BA?
Switching to BA