Now, as someone from the UK, I would say it's not as simple as the UK says kickers and the US says panties.
Knickers, I have to say, is a bit of an old term amongst me and my age bracket. At least in my social circle. My Aunty wears knickers. My partner is probably more like to call her underwear her "pants".
We've discussed it before and it seems to us that saying "panties" is a bit cutesy and makes us sound like we're trying to be Americans. Just shortening it to pants (as a UK person I've always called my underwear my pants) feels much more natural to us.
But, over all, I like how knickers is good for the right character. Like a strict Governess, wielding a cane, who demands her insulant student hitches up her skirt and pulls down her knickers.