The request comes from somewhere else
Almost nobody wakes up wanting a legalised certificate. The job arrives as a line in someone else's letter: send us a legalised birth certificate, or we cannot go further without a legalised marriage record. Because that line is written by a person who deals with many countries at once, it is rarely precise about the route, and the precision has to come from your side instead.
The route does not bend to the purpose
Sierra Leone has not joined the Hague Apostille Convention, so embassy legalisation is required whether the file is for a job, a school, a bank or a family matter. The stages are identical in every case. What varies is only the list of papers, which is why the first useful question is what the far end needs rather than how the process works.
Choosing the list of papers
Edinburgh Registration Service at City Chambers, 253 High Street, Edinburgh EH1 1YP, prints certified extracts of Scottish births, marriages and deaths, and a fresh extract is a signed record rather than a keepsake. Order every extract the request could plausibly cover in one go. An apostille from United Kingdom to Sierra Leone is charged per paper, but the waiting is shared across the envelope.
Why a spare copy is cheap
The British stage costs £45 for each paper by post, or £40 for each paper on the faster lane open to registered businesses. A second copy therefore adds a fee but no extra weeks, while learning later that one more paper was wanted adds the fee and the whole timetable again. With a consular stage waiting at the end, that second timetable is the expensive part.
English, and getting it there
English is the official language of Sierra Leone, so a Scottish extract can be read as issued and no translation has to be commissioned. Document legalisation for Sierra Leone therefore comes down to the papers and the post. Move the bundle on a tracked service, keep a scan of every sheet, and the person who asked gets something they can act on.