Buckingham Palace

Buckingham Palace is one of the Scenes you get as a reward after completing specific parts of the Oliver's Teapot questlines that were released with the Silver Teapot Event in Hidden Chronicles. After the player unlocked these they will still be available even if the Event ended. The Scenes can be found after clicking on Ramsey Manor and then choosing the Featured tab.

Super Clue
The Super Clue wants you to polish the Teapot. To do so, you have to take the Rag, dip it into the Silver Polish and use it on the Teapot