The Biltmore Mayfair is a high‑end hotel that opened at this address in 1969 (originally as the Britannia Hotel) and re‑launched under the “Biltmore” brand after a major renovation that finished in 2019.  
The hotel sits on the northern side of Grosvenor Square, a prestigious 18th‑century garden square with a long diplomatic and aristocratic history.
The current Biltmore building surprisingly only dates from the 1960s (designed by Richard Seifert), Grosvenor Square itself is much older laid out in 1710 by the Grosvenor family as part of their Mayfair estate.  
 
Interesting facts..
The building stands on land once planned as a private London residence for the Grosvenor family, laid out in 1710, long before it became a hotel address.  In that early phase the site was part of the aristocratic Grosvenor estate, it was originally intended to be a quite residential area.
The watercolour shows the central bay of the North terrace