Acropolis Museum. Congratulations!
The Parthenon Marbles (sometimes called the Elgin Marbles) have been in British hands for over 200 years. These valuable cultural artifacts were and remain the property of the people of Greece. As many in the UK agree, it's past time to return them to Greece.
In the early 1800s, in the words of the British Museum, Lord Elgin "acquired" these sculptures from the Parthenon, purportedly having permission of the Ottoman Empire that controlled Greece at the time. Even if he had permission, this is like Germany giving away the Eiffel Tower while they occupied France during World War II.
No private museum could get away with keeping stolen property. Neither should the British Museum. Let them know.