I suspect they are intent on using them for their voodoo / witchcraft stuff, rather than running some sci-fi underground organ transplant operation in a terraced house in Milton Keynes, It's probably not for supplying Nigeria's equivalent of Dr. Christian Barnard... I mean, some of these sort of people still like to eat fellow humans' bits and bobs.
Yeah, that sounds more likely. While there might be some dodgy Drs in the UK willing to perform such an operation a transplant needs full-on hospital facilities, support staff etc. for More likely to happen in **** hole countries like Egypt and China etc.
Some Nigerians (regardless of whether they're nominally Christian, Muslim etc...) can go a bit tribal, ritual child sacrifice or some voodoo nonsense with the organs seems more likely here.