Apostille vs. Embassy legalisation for Iran
A country can prove a foreign signature to itself in one of two ways. It can join a treaty and take one standard certificate from every other member, or it can keep an officer of its own in the loop and read the file directly. Iran does the second, and an apostille for Iran is simply not the instrument that route runs on.
Iran's Hague status & what it means
Iran has not joined the Hague Apostille Convention. An apostille from the United Kingdom to Iran therefore carries no weight there, and the gap cannot be closed from this end by doing more of the same thing. Only a shared treaty would close it, and only the two countries could make one. Everything else is effort spent on the wrong half of the journey.
Extra paperwork is not a substitute
The instinct after a refusal is to send more: another certified copy, a letter of explanation, a second British stamp above the first. It is a reasonable instinct and it never works, because the receiving side is not counting sheets. It wants one particular mark, applied by people it deals with, and no quantity of anything else stands in for that.
The cost of the instinct is real. Each extra document on the British side attracts its own charge, each addition slows the envelope down, and none of it advances the stage that actually decides. A thin, correct file beats a thick one on this route every time, and it reaches the consular desk sooner as well.
Cost & timing for this route
The British charge is published: £45 for each document by post at the Legalisation Office, or £40 for each document on the next-day route open to registered businesses. No consular figure appears on this page, because that side sets its own. Since the second charge is the unknown one, spending on optional British extras burns money against the half of the job you could already forecast.
Destination-specific requirements
Iran asks for consular legalisation, applied by the officials who represent it in Britain. They look at the document, so its quality is what repays attention: for a civil record, a fresh certified copy from Plymouth Register Office at Derriford Park, drawn from the register itself. One good sheet, sent down the right route, is the whole of the preparation worth doing.