I have some sympathy for these "queue jumpers". I've often politely lined up in the priority line only to find when it really is enforced that people ahead get told to wait. This causes more of a "huddle" rather than line which I do tend to bypass on the assumption that the "stragglers" simply want to already be at the front when their boarding is announced.

If 75% of the aircraft has priority boarding, then there is no priority boarding any more. And, if you think BA is bad, try flying Lufthansa. There everybody feels like they should have priority and it is policed even less than BA do.