I wonder if some of the Brits who use the phrase "step up to the plate" don't even realize it comes from baseball.

I agree that, if they wanted to use a sporting metaphor, "step up to the wicket" would make more sense in a purely British context.

Maybe they're thinking of dinner plates, but then wouldn't they say "sit down to the plate"?

I guess it goes to show you don't need to be familiar with the origin of a saying in order to find it useful.

Another example: "the whole nine yards." Nobody really knows where that came from, although there have been a lot of theories kicked around. Yet it became very popular among people who didn't have a clue.