A bit more info on date of Moncrieff's office in London, the two images below are from the Monart archives in Perth Museum. The important bit is the badge on the heading " NATIONAL SCHEME FOR DISABLED MEN". This scheme was introduced in 1917. This would indicate that the Moncrieff office in London was pre 1917 as the headed note paper with the London address does not have that emblem. Also the later headed note paper is minus the London address.
Thanks for the links flying free, pretty swanky building in an up market area of London.