The mark has no address you can visit
It surprises people that the stamp itself has no shopfront anywhere. The Legalisation Office issues every British slip from PO Box 6255, Milton Keynes MK10 1XX, and it deals with senders through the post rather than across a desk. There is no queue to join and no slot to book, so nothing in this route depends on your diary.
What is genuinely local to you
The local part is the paper. Westminster Register Office at 317 Harrow Road, London W9 3RJ issues fresh certified copies of birth, marriage and death records, and that copy is the sheet you should let travel. The certificate in your own drawer stays with you, which matters because a lost civil record is replaced only by starting again.
For anything that is not a civil record, the local end is wherever that paper already lives: a school office, a company's own files, a solicitor's drawer, a court. Collect the signed version from there and stop. None of those places issue the slip, and none of them need to know where the paper is going next.
One stamp, then the envelope home
Senegal joined the Hague Convention in 2023, so this corridor takes a single stamp. Document legalisation for Senegal is complete once the slip is attached, and an apostille from United Kingdom to Senegal is not followed by a consular stage anywhere. The whole job therefore lives inside the British postal system from the day you begin it.
Planning a job that happens in envelopes
Because every step is postal, the days to count are the days out, the office's own line, and the days back. The published charge is £45 per document by post, or £40 per document on the next-day line for a registered business. That figure buys the mark itself and not the travelling either side of it.
So what you need for an apostille for Senegal is an address the office can reply to, a signed public version of each paper, and the charge for each one. There is nowhere to turn up in person and nothing to hand over by hand. That makes this an easy job to run from a desk, or from another country entirely.