>>71324133570% of stairs in the UK are clockwise.
https://www.researchgate.net/publication/279496087_The_spiral_stair_or_vice_Its_origins_role_and_meaning_in_medieval_stone_castles
This article was linked on a page that was trying to debunk the idea.
It's very clear that stairs were designed to be fought inside of, even if such events did not occur often. Suppposedly, it's also common for these tower stairs to also have irregular step lengths and heights, which can only be explained as a defensive measure.
This sort of engineering is not exclusive to Europeans castles. On Japanese castles, they made the floor loud and cranky on purpose, so nobody could possibly sneak around inside of it.