One word, two very different journeys
People use the word apostille for any foreign stamp, but it names one specific thing: a single slip that Convention countries read without asking for more. Everything outside that arrangement is consular work, a chain that ends at a foreign desk. Document legalisation for the Democratic Republic of the Congo belongs to the second group, and its length is the reason planning matters here.
Where the destination stands
The Democratic Republic of the Congo has not joined the Hague Apostille Convention. An apostille issued in Derby for use in Democratic Republic of the Congo is therefore refused as a finished article, no matter how correctly the British half was done. So an apostille from United Kingdom to Democratic Republic of the Congo is never the whole answer; it is at most the first of two marks.
The measurable half
Derby Register Office at Riverside Chambers, Full Street, Derby DE1 3AF issues fresh certified copies of local civil records, and that copy is what travels. The FCDO Legalisation Office, PO Box 6255, Milton Keynes MK10 1XX, adds the British mark and posts the bundle back. Both ends of this half are postal, both are priced, and neither depends on anyone abroad.
A firm number and an allowance
The published charge is £45 per document by standard post, or £40 per document next-day for registered businesses, and it follows each sheet you send. Beyond that the spending is open-ended, since the consular stage carries its own official charge. Anyone asking what you need for an apostille for Democratic Republic of the Congo is really asking about two budgets, only one of which can be totalled today.
Blocks of time, not dates
A plan built on dates breaks the first time a stage runs long, and on this route the long stage is the one you cannot measure. Build it in blocks instead. Give the British half a slot, leave the consular half as an open block behind it, and hang no travel, no filing and no appointment on a paper that has not yet come back marked twice.