Ever since BMI pulled out of the GLA-LHR route the BA flights have been rammed and it's been much harder to get the cheaper tickets, in my experience. I bet this route is highly profitable for BA these days.

Once BA have consolidated the remaining BMI domestic routes I would expect to see the same thing happen. So all you ex EDI or ABZ people make the most of the cheap fares while you can - before the flights/capacity are consolidated and BA has a monopoly on these routes.