There's a more substantial support in the center behind the bars and you could add some 3m mounting tape to the equation. I hate the idea of putting holes in the bumper but they are always going to be covered by the plate anyway and don't want to worry about the car wash knocking it around..... No screw holes that way, my only concern is that the thin vertical bars should be the only thing supporting the holder and license plate.
European license plates should provide more protection because they're wider than North American plates.I was surprised too, seems unfinished. Here's how the USA license bracket sits, if the UK is in the same place your plate may give pretty good protection. (Mine has two clips that grab the vertical bars in front of the condenser and unfortunately requires two screws on top in the bumper).
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I believe this is a feature Mazda call “active air shutter”