Lots of interesting (and valid) points raised but many not applicable to the specific situation that inspired my vent. As far as I could tell, the issue at E71 last night was down to two things:

a) Poor gate layout design, with the Zone 1 lane closest to and right up against the 'entrance' area to E71 and E72. So as passengers approached the area and saw a crowd already gathered, they understandably add themselves to the mess, thereby further crowding the Zone 1 lane.

b) Willful ignorance on the part of some passengers, which IME tend to be Zone 2. Those in Zones 3 to 5 tend to either not know or not care about priority boarding, so have no trouble following fairly simple instructions. IME, Zone 2 is full of people who have paid for or earned some kind of 'special treatment', but don't fully appreciate the various levels of 'special' AC parcels out, and therefore feel entitled to be at the front of the line.