I thought the whole purpose of an alliance, such as oneworld, was to fly your own passengers out to a regional hub from where they would be taken to the final destination.
Thus if BA receives its passengers at LHR fed from other ports, it then flies them on to Doha, Colombo and Kuala Lumpur. From there they would be transported to Goa, Thiruchirapalli, or Manila whichever the case might be. This would be done by codeshare or some other revenue sharing agreement and thus reduce the loss of clientele BA would otherwise suffer, since it does not serve the said destinations.
That is why I do not understand why BA does not already codeshare with Dragonair onwards from Hong Kong or with Lan from Lima etc. Or do I completely misunderstand the situation?