Apostille vs. Embassy legalisation for Finland
Two routes exist for proving a British signature abroad. One is the apostille: a single certificate that countries inside a shared treaty accept from each other without further comment. The other is the older consular chain, with a second officer reading the file before it counts for anything. An apostille for Finland is the first kind, so one office holds your paper and the gap has one part rather than two.
Finland's Hague status & what it means
Finland joined the Hague Convention in 1985, and the United Kingdom sits inside the same treaty. Because both ends are covered, an apostille from the United Kingdom to Finland stands complete and nothing is added to it later. For planning that matters more than it sounds: a second stage would mean a second body holding the sheet, and a second stretch of doing without it.
The Plymouth → Finland route step by step
Decide first which sheet is going to travel. For a civil record the answer is a fresh certified copy from Plymouth Register Office at Derriford Park, drawn from the register and carrying the same weight as the one you keep. Order it, and the certificate in your drawer never has to move at all.
The copy then goes by post to the FCDO Legalisation Office at PO Box 6255, Milton Keynes MK10 1XX. That office covers the whole country and works through the post, so the wait in Devon is the wait anywhere. It returns the certificate joined to the sheet it was issued against.
Cost & timing for this route
The charge is £45 for each document by post at the Legalisation Office, or £40 for each document on the next-day route open to registered businesses. Time is the part no figure here pins down, because two postal legs and the office's own handling all feed into it. Build the plan around a stretch you can live without the paper, rather than around a single date.
Destination-specific requirements
Finland takes the certificate as issued, with no embassy stage and no second fee to allow for. That holds the whole matter inside one round trip: out, marked, home. The only thing left to manage is your own calendar, and the cheapest way to manage it is to make sure the sheet in the post is one you could replace, never the one you could not.