The first floor was completed in September 1930 and work continued at the astonishing speed of a floor a week, with the roof completed in November 1930. Unusual steps were taken to ensure effective soundproofing of the hotel. The floor and ceiling of each bedroom were lined with compressed seaweed while the outside walls were lined with cork. Accommodation was designed to be flexible. Guests can occupy a number of rooms, using interconnecting doors, without need to use the corridors.
All rooms have a private lobby, while the suites have a private hall as well.
The original Sherry Bar, in Spanish Renaissance style, was closed in 1938 and an American Bar constructed on the Park Lane side of the Hotel. In 1952, one of the wings on the Deanery street side was extended from first floor level, adding another 30 single bedrooms. On the seventh floor above these rooms was built The Oliver Messel Suite - the first luxury suite ever constructed in London. This entire wing and The Oliver Messel Suite were opened in time for the Coronation of Queen Elizabeth II in June 1953. A further four luxury suites, built on the roof, were completed in 1956.