Lester---
It would seem that the booklet you have is from the 1929-1932 time frame. The Leadenhall Street address is Royal Mail House, which was White Star's principal office from 1 July 1929. Before that, the principal office was on James Street, Liverpool, and the London office was Oceanic House on Cockspur Street.
On 4 November 1932, as the Royal Mail Group was being dismantled, White Star's registered office was moved out of Royal Mail House and back to Oceanic House.
Sources: Anderson's White Star; Mallett and Bell's The Pirrie-Kylsant Motorships.
MAB