I believe that The International Sporting Club was in Berkeley Square then moved to 45 Park Lane. Closed for a "refurb" and reopened as the Colony!
As we all know, Crockfords was opened at 50 St James and then obviously 50 St James/50 (Old Ritz) used the building later.
Got a few matchbooks from the ISC but not one with the 50 address but......maybe the building was used for another casino inbetween...anybody got any ideas?