Circle One Surfboards are a UK board company based in Crediton Essex, the fin system is a US system DFS a sticker near the fins on the board.
It is always good to go to the Brand name makers for first hand advice.
The DFS boxes are pretty much a fin system from China no matter what the patent letters say they will take Standard FCS fins and with a little work solid base Futures, the usual FCS change is M5s but it you can access secondhand fin sets you can play mix and match.
Gentle poke though

have you ever thought to read the various labels on the board, they can take right to the source!
Usually glassed in not the ego one stuck on.

I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷