There shouldn't be a problem with you entering the UK on your UK passport. The issue would only arise if you tried to enter on the (now technically invalid) visa. If you think there might be a problem, go through the manual checkpoint upon arrival in the UK and ask the UKBF official to cancel the visa. If they can't do it there and then, they can probably tell you if it poses an issue and if so, how to proceed.
EDIT: I assume that what you have in your Nigerian Passport is a Visa issued before becoming a British Citizen. If it is, instead, a "Certificate of Entitlement" (not actually a visa) that proves your right of abode in the UK, then it is valid until expiry and poses no problem whatsoever to entry into the UK.