One mark, and the route is done
Japan joined the Hague Convention in 1970, which means a British public paper carrying the right certificate is ready to use there without a further stage. An apostille issued in Brighton for use in Japan is the complete answer, not a first step towards one. That fact removes the consular desk that lengthens so many other routes, and with it most of the uncertainty about time.
Because the process has one certifying stage, the questions worth spending effort on shift. There is no second authority to satisfy and no separate queue to join. What is left is arithmetic: how many sheets you are sending, and at which of the two published rates. Getting that right in advance is most of the planning this corridor needs.
The two rates, and who each one is for
The Legalisation Office (Foreign, Commonwealth & Development Office) publishes £45 per document for the standard postal service, and £40 per document for a next-day service available to registered businesses. Those are the only two figures on this route from the British side. Everything else you spend goes on postage, on any certified copies you order, and on nothing else at this stage.
The shape of that pricing catches people out, because the quicker rate is also the lower one. It is not a discount for being in a hurry. It is a different arrangement with a different set of users behind it, and eligibility is what decides which door you go through. Someone acting in a personal capacity uses the standard postal rate and plans a longer wait around it.
What the charge is attached to
Each charge covers one document. That sounds obvious until you have a bundle in front of you: a birth record, a degree and a company resolution are three papers and three charges, however neatly they sit in one envelope. Knowing what you need for an apostille for Japan is therefore partly a counting exercise, done before you post rather than after the invoice.
The count also decides how much preparation you do locally. If two of your three papers are civil records, Brighton & Hove Register Office at Town Hall, Bartholomew Square, Brighton BN1 1JA can issue fresh certified copies of them, and those copies travel instead of the sheets you keep. A certified copy costs something, but it is cheaper than replacing a lost original.
Reaching a real total before you start
Set out the sum in the order the money leaves you. First the certified copies, if the records are civil ones. Then the per-document charge multiplied by the number of sheets. Then postage in both directions. Document legalisation for Japan needs nothing beyond that on the British side, so the sum you write down is close to the sum you will actually pay.
That certainty is the quiet advantage of this corridor. An apostille from United Kingdom to Japan has a known price per sheet, a known issuing body and a known finishing point. The only thing you cannot fix in advance is the post, so leave slack for the envelope rather than for the desk that handles it.