The form of the cross, the interlace patterns and the bosses are definitely Celtic. Though the interlace is not perfect. Usually when you follow the thread you get an endless pattern symbolizing eternal life. Here you have two distinct threads intertwined. The figures on the bottom could be Jesus arrested by two soldiers. And just above it Mary with the baby with a bishop on the left (one of the sages?) and on the right maybe Joseph (?). The animals don't fit into the imagery either, usually you have the lion, the taurus, a man and the eagle for John, Luke, Mathew and Mark.
I offered a rather complete interpretation of the figures three posts earlier after a bit of research. I'm guessing you missed it. If you think I was off (I could be), please share your opinions. I'm going with the principle that if there are figures on a high cross representing scenes in the Bible, all the figures do. I'm not aware of a tendency to mix different sources except when it came to decorative art like knots and vines.Very interesting, maybe we get a post from someone who can solve this riddle.