Basically the marbles were stolen decades ago, and the argument was that Greece was in no shape to hold them, so England was protecting them. Now we have the Acropolis museum, that argument doesn't hold so well any more.
Just to make the history clearer, they were taken centuries ago -- they were taken to Britain between 1801 and 1812.
I saw it in (I think, it wa sa while ago):
Posters in the airport
Museums
Tour Guides
Random conversations
So some touristic and some just random like airport and people