To add insult to injury MAN pax usually pay a hefty premium to be first in line for the chop. I recently checked a MAN-LHR-SIN , HKG-LHR-MAN J class ticket with BA, it was almost £1,000 cheaper to originate the same trip with BA from AMS rather than MAN.
Actually that's pretty standard industry practice. AF CDG-LHR-LAX was packed full of US bound French passengers as it was sold WAY cheaper than the CDG-LAX service which involved two less aircraft to get you there. It's how the legacy / hub airlines sell outside of their home market. Other UK home markets are in the same boat and this is not specific to BA or MAN.