London will be looking for a low-cost feasible bid.
That's the trouble. This project is an extreme example of a government style where they can eventually find the substantial funds for capital investment (building the airport) but then show extreme parsimony in funding the continuing operation (running a service). I'm sure there are some in government who cannot understand why commercial operators are not falling over themselves to provide a service, and there will even be a few who want to apply some form of tax/charge to it to recoup the capital investment. Completely divorced from reality.
It does seem that Comair have got commercial cold feet over the thing, and it also seems that Comair have been the only operator who seem to have had difficulty landing there. I presume that South Africa has relatively benign weather, and their crews have little experience of Funchal, Sumburgh, or other comparable places. Their "special" 737, which actually just seemed to be a standard one, seems to have been happily deployed on their internal South African routes equally with the rest of their fleet. There's little medium-haul charter capacity available in southern Africa, but presumably someone will eventually pick up the reins once enough financial support is provided.