Don't forget that the reason Eastern decided to fly to Bristol was largely due to 2000+ Orange personnel working 5 miles from MME, and a large Orange HQ being based near Bristol - so a lot of travelling businesspeople on a regular basis. I wouldn't be surprised if Orange have even come to some sort of arrangement where they block-book seats on each service.
I don't know the truth behind it, but I was once told a similar deal existed with Shell (or a similar oil company) arranging seats with Eastern on flights such as MME-ABZ and HUY-ABZ. I know Shell employees who use the service on a regular basis.