From the Historic England entry:
“…part of a group of riverside buildings of considerable monumentality, from Shell-Mex House to Brettenham House of 1931-2 alongside Waterloo Bridge, with which the Adelphi has group value…
The construction of the office block required an act of Parliament (the Adelphi Act of 1933) due to the covenants on the site imposed by a statute of 1771 relating to the original development of the area by John, Robert, James and William Adam from 1772 (Adelphoi is Greek for brothers). The Act gave permission for the demolition of 24 Georgian houses built by the Adams, as well as placing conditions on the height of the new building and requiring the developers to maintain and widen public thoroughfares. The demolition, which occurred in 1936, was one of the C20’s most notorious of an historic building and it invigorated a nascent preservation movement; the loss of the Adelphi is regarded as one of the watersheds of early conservation history. Houses in the two side streets (Adam Street and Robert Street) and in John Street (now John Adam Street) are all that survive of the original development. The new office building was originally called the New Adelphi, the building is now known simply as the Adelphi.
The design and detailing of the building are strongly Moderne or Art Deco, a popular idiom for commercial buildings at this time.
Much of the carved stonework is figurative, but there are also four giant allegorical relief figures on the corners of the Embankment front, representing west-east: ‘Dawn’ (by Bainbridge Copnall), ‘Contemplation’ (by Arthur J Ayres), ‘Inspiration’ (by Gilbert Ledward), and ‘Night’ (by Donald Gilbert). In scale and visual power, the four allegorical figures along the riverside are impressive. Carved under the direction of one of the foremost interwar British sculptors, Gilbert Ledward, the four sculptures are one of the few remaining architectural works by him in situ. Also important are the carved reveal panels to the entrance doors on John Adam Street by Newbury Abbot Trent depicting scenes of industry. Other sculpture includes carved coats of arms of UK cities at ground floor level to the east and west elevations, and smaller panels on a variety of themes including the signs of the zodiac, agriculture, and industry; the artists of these features are unknown, but their abundance, period character and considerable charm contribute to the interest of the building. The lettering above the entrances, in sans serif capital letters, was executed by George Manswell.
The building incorporates a roadway and promenade on the south side (known as Adelphi Terrace) with views across Victoria Embankment Gardens (see image) and the river. A garage undercroft takes advantage of the slope down to the Thames to allow vehicular access at street level from Savoy Place…”