Long haul fares are often much cheaper from distant airports than from the LHR or MAN. I live in Spain and a C class fare to Asia from my local airport using IB regional to MAD, than BA to LHR and onward to Asia, often costs me up to £1,400 less than a colleague flying BA MAN/LHR/Asia (the long-haul sector being on the same plane on the same day). The economics long-haul airfares!