Mr. Pitt

He is in charge of the Party in the United Kingdom, or at least the Party's mission there.  He sends "parcels from Harrod's" to the letter writer on a regular basis; in fact, the letter writer mentions explicitly that Mr. Pitt was responsible for organizing the entire trip to America.  It seems that Mr. Pitt serves as some kind of intermediary between the Party in America and other countries.  He operates from an office adjacent to St. Paul's Cathedral.  He is a man and he smokes a pipe.

Mr. Disraeli

Mr. Disraeli meets the letter writer in Southhampton and accompanies him or her on the train to London.  He takes the letter writer on a tour of Buckingham Palace.  There is no textual description of Mr. Disraeli.