Among the directions for the Family Activity Trail (ages 7-11) at the museum, there is this:
4. Diamonds are forever
Find the case with the crowns in it.
It is near the motor taxi.
Queen Victoria ruled over an empire that stretched all around the world. In 1897 Londoners lined the streets to celebrate the Queen’s Diamond Jubilee.
No matter what I put into the search box, that is the only reference to crowns I can find, but it must indicate that the Museum of London still exhibits some crowns!