Which route applies for South Sudan
An apostille is a single certificate that Convention countries accept from one another with nothing further attached. South Sudan has not joined the Hague Apostille Convention, so that route is not open. Papers going there need document legalisation for South Sudan: the UK certificate, then a consular stamp added by the desk that acts for the country. Both marks have to be on the file when it arrives.
Each handover closes a door
Think of the route as a relay rather than a form. At any given moment exactly one body has your paper, and that body decides what can still be done to it. While the sheet is on your table, spellings, dates and the choice of which record to use are all open. The register office prints what the register holds, and after that the text is settled.
The next door closes at the UK stage. An apostille issued in Newcastle upon Tyne for use in South Sudan binds a stamp to one specific sheet, and after that the two are read together. Swapping the underlying paper means the stamp no longer belongs to it. This is why a careless choice of source document is expensive later and free today.
The Newcastle upon Tyne leg in detail
Newcastle Register Office, at Civic Centre, Barras Bridge, Newcastle upon Tyne NE1 8QH, is where a civil record is re-issued, so your own certificate never has to leave the house. Papers signed by a court, a school or a company begin with whoever signed them. The FCDO Legalisation Office then takes over at PO Box 6255, Milton Keynes MK10 1XX, working entirely through the post.
What you need for an apostille for South Sudan, at this stage, is a signature the office already recognises and a sheet that has not been altered. It reads the signing, not the meaning, so nothing it does repairs a wrong record. Write your return address plainly, because the file comes back to you before it moves on.
Cost, timing and the last handover
The UK charge is £45 per document by standard post, or £40 per document next-day for registered businesses. An apostille from the United Kingdom to South Sudan is only the first custody stage, so the consular charge sits on top and is set by the mission that applies it. Timing works the same way: each holder adds its own days, and the total is the sum of three separate queues.