Start with New Bond Street and you will only be a few hundred yards away from Piccadilly where there are now many coffee/patisserie shops as well as Richoux, Peyton & Byrne at the RA, Fortnum's or the Ritz - you can pay your money and take your choice.
Hermes Royal Exchange in the City is smaller but has a lovely manager.
Ideal if you are using the train into Liverpool Street Station.
Hermes Sloane Street is walking distance from Hermes in Harrods.
And there is also Hermes in Selfridges.
London is well- served.
I find all the staff very helpful; i was looking for something specific in NBS and they did a search and located one for me in Royal Exchange.