One slip, or two marks
Treaty members honour each other's stamps on sight, which is what makes a single slip enough between them. Outside that circle a state prefers its own consular officer to look at the file. Nigeria works the second way, so a British paper collects one mark here and a second from the receiving side.
Nigeria and the Hague Convention
Nigeria has not joined the Hague Apostille Convention. A British paper bound for Lagos, Abuja or Port Harcourt requires embassy legalisation on top of whatever the Legalisation Office has already applied. The United Kingdom is a treaty party, which is why the stamp exists here, though membership at one end alone changes nothing at the other.
The Sheffield side of the work
The British stage runs entirely by post from one address, so there is no counter in Sheffield to visit. The local task is gathering the source: the Register Office at the Town Hall for civil entries, a university for a degree or transcript, a professional body for a registration, and a solicitor for a private company paper.
An apostille from United Kingdom to Nigeria is often part of a set rather than a single errand. Qualification checks ask for the degree and the transcript behind it, and company registrations ask for several corporate papers at once. Posting them together keeps the marks aligned and gives the consular desk a single, coherent file.
English, and the business behind the paperwork
The language question that dominates most of these routes barely arises here, because English is one of Nigeria's official languages and a British certificate can be read on arrival. That saves a step and a cost. It also concentrates attention on the stamps themselves, since nothing else about the paper needs explaining to the office receiving it.
Traffic on this corridor leans commercial and professional. Degrees, transcripts and chartered memberships travel for jobs in oil, banking, health and engineering. Company records follow for firms registering a Nigerian entity or bidding for work. Family papers move behind them, supporting residence, schooling and inheritance, and take exactly the same two-stamp path.