The 135,000 figure is the pax routing through LHR.
135,000/year = 370 pax per day flying MAN-LHR-HKG
Tomorrow there are 14 MAN-LHR flights (counted off the Manchester Airport website) on A320 type a/c with an average load of 100ish gives us 1400 pax.
If 370 of these go to HKG, that's roughly 25%. Given that most of that 25% will fly BA MAN-LHR-HKG, I think they're definitely missing a trick there!!
I'm not saying your wrong, but unless my maths has gone a bit awry, I can't see how this would work!
they'd find a way to make it not work as per normal BA practices
Its an argument that goes perpetually around on here, but if regional medium/longhaul worked for BA they would do it. All BA do is fly to their hub from MAN, just like LH, EK, QR, EY, AA, DL, CO, LX etc.
Britain is a small country and unless people are willing to pay exorbitant fares to fly on smaller/emptyer planes to various destinations, its just not going to happen.