Why nothing is stamped where you live
One office issues these marks for the whole country and it works by post rather than over a counter. So the errand is done in envelopes: a sheet goes out, a marked sheet comes back. Nobody here, and nobody in any other town, can hand a paper across a window and collect it later, which is worth knowing before a day is set aside for the trip.
What the city does supply
The local contribution is the paper, and it is not a small one. Stoke-on-Trent Register Office holds birth, marriage and death entries for the area and prints fresh certified copies signed by a registrar. That copy is the sheet that travels, while the certificate you already own stays in the drawer where it cannot go astray in transit.
Where a sheet is not a civil record at all — a degree, a company file, a trade ticket — it comes instead from the body that issued it. Either way the local job is the same: put an official signature on a sheet you could replace if you had to. Everything after that point is identical for everyone, wherever in the country they happen to live.
The stamp that follows the British one
Guinea has not joined the Hague Apostille Convention. Outside that agreement the older chain of stamps still runs, so the British mark is followed by a consular one added here on Guinea's behalf. An apostille from United Kingdom to Guinea therefore lands in Conakry as a single item carrying two marks, and it is the second of them that the receiving desk is really watching for.
Money, and how many days to allow
The British charge lands on each document rather than on the packet, so the thickness of the pile sets that part of the bill. Days are harder to pin down, because a file on this route sits in the post twice and in a consular queue once. Start early and the distance from Milton Keynes stops mattering altogether.