Great Britain Philatelic Society

I have recently become interested in the pre-stamp era and have a query that has been puzzling me (apologies if it seems very basic): Was there only one Chief Office in London at any particular time? I have read that there was a Chief Office in the early days in Bishopgate, then Lombard Street, then in 1829 at St Martins-le-Grand and at one time in Throgmorton Street but I am not clear whether these were all for the General Post or whether different Chief Offices were used by the Local Post. I do know for example that the Chief Office at St Martins-le-Grand acted as the Chief Office of the Twopenny Post (ie Local Post) but was it also Chief Office of the General Post at the same time? I am wanting to structure my admittedly embrionic collection logically so do not want to mix up things incorrectly. Any comments would be appreciated as I am on quite a learning curve.
John