Every desk checks the mark above it
Document legalisation for Angola is a run of small, narrow acts. Each office looks up, at the signature or stamp the previous office left, and confirms that it is real. None of them looks down at the words of your document. That is why a file with a gap in it fails even though every sheet inside it is genuine.
Where Angola stands
Angola has not joined the Hague Apostille Convention. That treaty replaces a chain with one certificate, so where a country stays outside it, the chain is what remains. There is no apostille issued in Reading for use in Angola that shortens this, and no faster version of the same idea sold under another name.
The order is the whole design
Because each desk only recognises the one before it, the sequence is not a queue you can jump. The British certification by The Legalisation Office has to exist before consular officials have anything to attach their stamp to. An apostille from the United Kingdom to Angola would not fit that slot, so the file simply stalls where it started.
What the British stage costs
The British stage is charged per document, at £45 for the standard postal service. Per document is the phrase that matters: five sheets are five charges, not one. So the honest way to plan is to cut the list before anything is sent, rather than adding papers later and paying the same charge again for each one.
Planning it as one run
What you need for an apostille for Angola turns out to be a plan for a chain rather than a single errand. Work out the whole sequence first, get every sheet into the same shape at the same time, and send them as one file. A chain run once is far quicker than the same chain run twice.