Apostille vs. Embassy legalisation for Cuba
Cuba has not joined the Hague Apostille Convention, so no British certificate on its own turns a paper into something usable there. Anything sent that way needs embassy or consular legalisation instead, and that is a separate act by a separate body. No apostille issued in Glasgow for use in Cuba amounts to a completed set, however tidy the British half of it looks.
Cuba's Hague status & what it means
Inside that treaty a paper is settled once and read the same way at both ends. Outside it, the set is assembled layer upon layer, each layer naming and describing the one under it. What you finish with is a physical object carrying its own history, and a history of that kind cannot be reprinted on demand.
The Glasgow → Cuba route step by step
The FCDO Legalisation Office at PO Box 6255, Milton Keynes MK10 1XX works entirely by post and returns the set to whoever sent it in. There is no counter to visit and no way to collect. That return is ordinary practice rather than a hitch, and it means the joined bundle sits in your hands between the two stages.
Treat that as custody rather than as a pause. Document legalisation for Cuba runs on one physical object, and you are the only party holding it while it waits. Nothing needs doing to it, which is exactly the risk: an idle bundle gets moved, folded into a wallet, or opened up so somebody can photograph a page of it.
Cost & timing for this route
The published British figures are £45 / document by standard post and £40 / document next-day for registered businesses, both met per document instead of per envelope, and a further official charge lands at the consular stage. Since an apostille from United Kingdom to Cuba is no more than the first layer, a ruined set means paying for both layers over again.
Destination-specific requirements
Everything about a Cuba-bound file rewards care with the physical set. Order the extract you need in the quantity you need before anything is stamped, because each sheet runs on its own and no mark can be moved across. Then keep the returned bundle exactly as it arrived, and hand it on in that state.