Balewa, Air Nigeria must have done their homework
First off, Egypt Air, because of the Arab spring, is suffering from reduced traffic, so it's offering it's aircraft for lease at reduced rates. So, there is a cost savings there.
Secondly, there IS a market for travel to London quite distinct from the body of Nigerians attracted to the BA brand. Price figures for these travelers. They fly Turkish, Libyan Arab (when they were here) and the like, and their numbers is considerable.
Remember too, that by the time Virgin Nigeria, this company's predecessor, suspended the London service, they had become number one in terms of numbers carried on the London route. And although that's quite a distinct matter from gross or net earnings on the route or yields per passenger, it does indicate that the potential for Air Nigeria is there.