http://www.ph.ucla.edu/epi/snow/1859map/map1859.html
That is a link to a map that is, I'm fairly certain, rather close to the map above, with a wider scope.
If you want to swap out this map for what's up there now, I would recommend, if possible, to utilize Rows J through R and Columns 10 through 15. (Grosvenor Square, where the Hughes' reside, is within the bounds of RJ-RL, C10-C12; the map currently used covers, I think, an area slightly South and to the West of that.)
Ah, yes… I think Waterloo Place is between Pall Mall and The Mall on the southern tip of Regent Street. Teeny tiny type, but if you squint, it's there. (RM, C14 on the map I've linked here.)
Hope this helps.