I know this is slightly out of the scope of 'Sydenham', but where is the official border of the county of Kent these days?
Some properties in Bromley still state Kent in their address but there is no mention of Bromley, Beckenham, etc on the Kent County Council Website, presumably as it is a London Borough. Telecom STDs are assigned Greater London - 0208. Postcodes however are BR, not SE.
I guess Border Road offers a clue to a boundary from days gone by...
I don't know, but for me we're right on the border! How do I know - half the people who ask for train tickets at the station ask for "Return to London" and it makes me wince. The other half ask for a "Return to Charing Cross" - which feels much more appropriate.