Hi
Just completed GLA<>LHR<>LIN and return. Never heard any pre-boarding for Gold etc.
I did ask at LHR as they were calling the LIN flight by row numbers, the BA staff member said I could board when ever I wanted too, which I then went and did, but next time I think i will wait as I was in 3d and got battered by near enough everyone coming onto the aircraft, must have a few bruises.
Good things for the whole trip was all the dedicated Gold/Silver/Business checkin desks and fast track. It really did work well this trip. Plus had some other nice things for me.