2.4Ghz is 2.4Ghz, it doesn't matter where you are. as long as they are 802.11b or 802.11g compatible, you're golden.
and more specifically, yes....U.S. wireless cards will work in the U.K., and vice versa. it's just those damned A/C power adapters you gotta watch out for....
i know this for a fact, as i support wifi hotspot locations in both the U.S. & the U.K.