I'm not British, but I can't imagine drinking Earl Grey anyway other than black.
I find that interesting that its hard to find.Despite what the writers of Star Trek: The Next Generation would have you believe, Earl Grey is generally considered tea for people that don't like tea. It's quite hard-to-find at decent (college, hotel) afternoon teas.
In the final episode, just before whatever final showdown with the entire enemy fleet (was it the Romulans? I forget. Oh, Klingons. I think that was it.) he should have ordered ...Tea. Earl Grey. Hot.