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I have previously done tight transfers from Heathrow to a local Finnish airport, via Helsinki - likely very similar flights to your own.
You need to go through passport control (automated gates seemed quickest, sometimes they also have a dedicated "short connection" lane). However, you do not need to go through a security check.
Finnair will put the gates for upcoming flights on the screen of your first flight, make a note of where you need to go and head straight there without delay and you should be fine!
Upvote:0
I had exactly this situation today: Coming from a Non-Schengen flight and transferring to a Schengen flight at Helsinki airport. Yes, going through security control was mandatory.